There are many misconceptions to unpack here. Jacob and Wilhelm Grimm (1785-1863 and 1786-1859, respectively) published their first volume of Kinder und Hausmärchen (Children’s and House Folktales) in 1812, based largely on material that they had collected. They did alter the folktales (i.e. Märchen) that they heard in several ways, not the least of which was that they abbreviated the original narratives. Without modern recording equipment, it was difficult to record long stories word-for-word. Typically folktales were extremely long, often taking more than one night to recount, so the Brothers Grimm were forced to work from their notes. The final product was shorter and certainly changed.

In general, the European folktale was reserved for adults - they were the adult novels of the day. They were told at night, typically after the light banter and the exchange of the news of the day - topics that would have been acceptable for children. Once children were put to bed, a storyteller would begin the telling of a folktale. This model is idealistic, and reality obviously took every form imaginable - and a few that can't be imagined! - but this is how professional folktale collectors consistently described the pre-modern setting of the telling of a folktale.

As a result of all of this, folktales were not only much longer than the Grimm's Fairytales, but they were often much more violent and sexual. Of course, we must keep in mind that these stories were retold and retold thousands of times, so there was no definitive version of anyone of these stories. With a time machine, we could no doubt find single retellings of each of these folktale types, told in a way to suit whatever argument we were putting forward to describe the "original form of a folktale", but that would not be true to the nature of the tradition.

It is true that sometimes gender roles were switched, but usually, most of the collected versions fall into one approach to the roles of the men and women in a given folktale type. And then we stumble on a strange outlier that flips those roles. Other than to say that pre-modern European society was intrinsically sexist by today's standards, there was nothing deliberately, insidiously crafted in these stories as a means of suppression of anyone. They were reflections to fit a society and culture, but that was the extent of it. Casting the Brothers Grimm into some diabolical role of super-oppressors is absurd. There is no evidence to support that and reaching back in time to find variants different from the ones of the Grimm collection doesn't prove anything. Folktales varied from place to place and time to time because that is the natural of oral tradition.

The folklorists are dissecting this nicely but one small detail that jumped out

Both brothers belonged to a small fanatical sect of Catholicism that vilified women because of the idea of Original Sin

The Grimm Brothers were brought up in the Reformed Calvinist Church and certainly did not convert to Catholicism.

Wait wait wait...honestly having this quote show up on this sub is genuinely hilarious to me because I know exactly where this is from. I legitimately had an argument with this person on Tumblr around three years ago over this exact statement. Talk about flashbacks. Essentially, everything this person said is horribly misguided at best and actively malicious at worst. The person in question had an active vendetta against the Grimm Brothers and an extensive argument did not change that in the least. Going down the list:

First, and I've detailed this before in the links so helpfully provided by u/Vespertine, there is no such thing as an "original" version of a fairy tale based in oral tradition due to the extremely complicated relationship between fairy tales and the historical record. We can talk about "older" or "more recent" versions, and we can talk about more and less popular versions, but there simply is no "original" version of a fairy tale unless it is a literary-based fairy tale such as the ones written by Hans Christian Andersen. The very nature of fairy tales is that they are fluid and ever-changing (ie, that they are never told the same way twice). Every version of a tale (whether written or oral) is as legitimate as the other, regardless of embellishment or changes of the text. There is no “true tale,” because there are so many different versions, even within a confined area.

Second, on the topic of Cinderella in general: the quote in question was a response to a tumblr post that was talking about 'Disney vs. Seven Early Versions of Fairy Tales'. It's therefore relevant to note that the version of Cinderella the Disney movie is based on is the (French) Perrault version; the Grimms version, Aschenputtel, is a Cinderella story containing two stepsisters, a ball, and the infamous cutting off of toes and heels incident, but a Grimms adaptation of Aschenputtel would look radically different than the Perrault adaptation we got in Disney’s Cinderella.

Cinderella is one of the oldest and most widely-spread fairy tales in the world. There are literally Cinderella tales from every part of the world (the oldest known variant is from Ancient Greece, and there’s Ye Xian, an early Chinese variant). The Perrault version was the one that introduced the glass slipper (before that, it was fur, generally, but the French word for fur was remarkably similar to the word for glass, so it became the glass slipper), the fairy godmother, the pumpkin, and a couple of other things, and is currently the most famous version of the story. The Joseph Jacobs version of Cinderella also includes the gruesome foot-cutting, as does the Norwegian version of Katie Woodencloak. The Scottish does as well, and the Greek version (Little Saddleslut) has the stepsisters getting hewn into pieces in the end. The Russian “The Little Birch” includes mutilation of the “sisters” as well, and there’s a Native American “Cinderella” that has the sisters being turned into trees at the end. A particularly memorable Chinese version has the stepmother and stepsister getting crushed by stones in the end, and The Story of Tam and Cam, a Vietnamese variant (and one of my favorites), Tam (the “Cinderella”) is actually killed halfway through the story by the mother and then is reincarnated in various ways, eventually getting her happy ending, and the evil sister is killed in a pot of boiling water at the end (at Tam’s request!). The “pecking out of eyes” thing was literally one of the only violent things that the Grimms brothers added to that story from the version they likely heard. Saying that the Grimm's version of Cinderella is more violent than its predecessors is patently ridiculous.

On Sleeping Beauty: The Sleeping Beauty assertion is also false, as a) Basile’s "The Sun, Moon, and Talia" (the story mentioned in the original post that this person responded to) is not a Grimms tale (and predates “Little Briar Rose,” The Grimms version, by almost 200 years, as does the wildly more popular Perrault version), and b) the whole point of the “Sleeping Beauty” fairy tale type is that the maiden sleeps. That’s the fairy tale type (Type-410). There are certainly variants where bandits are featured or where several events happen before the inevitable enchanted sleep that occurs in Type 410 tales, but as far as I am aware there is no Sleeping Beauty variant where she "outwits a bandit king and saves herself" unless they are talking about some contemporary subversion story that I have not read. To be perfectly honest, now that I've had three years to mull over that assertion, it almost sounds like they are talking more about a story like "Fitcher's Brid" or "The Robber Bridegroom" (both of which are loosely lumped in with Bluebeard tales) than a Sleeping Beauty narrative.

I actually cover changes the Brothers made to the tales in the posts helpfully already linked by Vespertine, but I'll add a little more here as well, just for further explanation and clarification:

The Grimms were trying to please two different audiences. Their first edition was not meant for children at all, and was instead a scholarly pursuit with them trying to record the tales faithfully, even down to colloquial language. It was only when people began buying the book and telling the stories to their children, complaining that the stories were too graphic in nature, that the Brothers rothers started extensively editing and sanitizing the tales. Many of the Christian references were added because of harsh criticism that they weren't Christian enough, for example. As u/itsallfolklore has already explained in their excellent response, fairy tales were not originally intended for the consumption of children, though children were sometimes in the audience, and as such included events of violence, sex, murder, rape, and other "child inappropriate" material.

I would also like to point out at this time that the assertion that the Brothers Grimm were the only ones whose tales were misogynistic in ways (and the fact that they are completely ignoring the tales of female empowerment that go hand in hand with the more misogynistic tales) is disregarding that there are several collections of tales that predate them that had the exact same themes. Basile, Boccaccio, Straparola, and Perrault, Madames d’Aulnoy and Beaumont...The Grimm Tales did not come out of nowhere.

Margaret Atwood actually has a really interesting quote about this:

“The unexpurgated Grimm’s Fairy Tales contain a number of fairy tales in which women are not only the central characters but win by using their own intelligence. Some people feel fairy tales are bad for women. This is true if the only ones they’re referring to are those tarted-up French versions of "Cinderella” and “Bluebeard,” in which the female protagonist gets rescued by her brothers. But in many of them, women rather than men have the magic powers.“

Whether or not I completely agree with this statement is a different question, but it's a good starting place to begin to recognize that the Brothers Grimm had several stories that featured girls and women with agency being clever, intelligent, and saving themselves.

In terms of the "cannibalistic queens and ugly stepsisters and the mass amount of violence against women" that supposedly didn't exist before the Grimms "wanted them to," it's just wrong. Flat-out. There are literally thousands of tales I could point out as examples that contradict this claim, some of which I already pointed out earlier in this response.

(Continued Below)

What's the origin of that quotation?

It's the opposite of what's usually said about the Grimms - a question which was answered a few weeks ago by u/erissays and u/itsallfolklore:
I've heard the Disneyified versions of Grimm's Tales Americans are familiar with are highly sanitized (RRHood and Grandma are eaten by the wolf,Snow White is about necrophilia,it's Cinderella's family, not steps- tormenting her, that kind of thing).Is this true? Were children the target audience?

You may also be interested in another set of answers, by u/integral_grail and u/erissays, to Were the tales collected by the brothers Grimm widely known before they compiled them? Did the more popular ones (Snow White, Cinderella, Red Riding Hood) match the ones more popular before they collected them? Were they immediately of academic interest?