I'm taking a history class that focuses on Theatre throughout the course of human history, and something that's been a surprisingly frequent occurrence in the last couple of months is theatre riots. These are things where the audience would get so impassioned by what they were seeing they would riot, be that because they agreed with the ideals of the piece, disagreed, or just really liked/disliked the actor.
The two examples that come to mind are the case of the opening of Victor Hugo's Hernani in 1830 (in Paris, I believe), which featured a riot between audience members who enjoyed the Romantic style and those who enjoyed the Neoclassical style, and the Astor Place Riots, which took place in Manhattan, and erupted because two companies were doing Macbeth at the same time, and fans of each of the respective Macbeths believed their choice was the best actor.
This isn't just a 19th century phenomenon, either, as just today we discussed a show (Six Characters in Search of an Author) which saw a theatre riot when it opened in Rome, though I didn't catch the year that happened. So what happened?
Sorry if this isn't the right subreddit for this question, but this does seem a history sort of question to me.
Well I've got good news and bad news, 1) most historical opera/theater riots weren't what we'd really consider a riot today, often it was just yelling and being rude, and 2) oh ho ho, they still happen! Lots of spicy and rude things happen at theaters globally. An opera riot in 2006 jumpstarted the career of one tenor and dinged the career of another one.
However you're quite right that there has been a general global movement towards simmering down at the theater, and "positive feedback only" to performers. You might find this old answer on crowd behavior at the theater interesting. But not only are riots almost universally unacceptable now, non-violent booing is pretty much unacceptable as well, outside of a few noble holdouts like La Scala, linked above. Consider one man's passionate plea for booing at the theater, where he blames the death of rowdy crowds on patrons becoming discerning customers, and customers wanting to reassure themselves they made a good economic choice by attending this particular art event (as enjoyment is subjective), and therefore, we stand and clap at the end of everything now, to applaud not just the performers, but also ourselves.