Titles a bit crude so let me clarify.
Apparently there was a moral panic about white people being enslaved around the 1920s and 30s, back when the Ottoman Empire was big and strong (IIRC), so they passed a law called the “White slave act” or Mann Act which was meant to fight that by outlawing the transport of women and girls for immoral purposes.
I plan on doing more research but based on the following it feels like there’s a racist agenda here, to put it bluntly. Since the two most significant uses of this law was to wrongfully accuse an innocent black person of raping a white woman.
First of all Jack Johnson, the American Boxer who suffered legally and financially because the law was invoked to present the relationship he had with his (White) wife as immoral and slavery with no attempt at provide evidence beyond “He’s black and she’s white”.
The other case, the Scottsboro boys, were accused by two white women of rape on a train, but long after they’re locked in jail for life, on it’s revealed these women were up and accosting black men for sex that train, and asking about their penises. After other white people realized, these two decided to accuse the boys because they were afraid the Mann act would be invoked on them.
Why would they be afraid of the Mann act being invoked on them if the law was passed specifically to protect them? The law does nothing to prohibit miscegenation or whites interacting with blacks.
I hope I’m completely wrong on this and there’s more to this law, but this has made me feel uncomfortable and is like to know more. Was there some kind of white supremacist agenda?
And a follow up question, did it just apply to white women or all women, in the way it’s meant to be used at least?
You have to understand that the Mann Act was primarily about outlawing prostitution.
The reason it was written about "transportation" wasn't really because there was a fear of women being kidnapped and transported elsewhere. It was simply because judicial interpretation of the time imposed much more limitation on the federal government's ability to regulate behavior. Adding the transportation bit was simply a loophole to allow federal intervention by invoking the ability of the government to regulate interstate commerce.
The primary point was to stop prostitution. For all the same reasons that some people are against sex work today. And with same mix of progressive sex-negative feminists, religious folk, and anti-female social conservatives behind it.
And yes, it didn't only apply to black men. There were also many cases of white men being hit. Charlie Chaplin being a famous example. And of course, there were plenty of non-famous people as well.
The reason it took on a racial tinge is because the law was interpreted a few years after passage to refer not only to prostitution, but to general sexual immorality. Adultery, seduction of a minor, anything that a puritan mindset might see as being against the sexual morality of the locality. And that's where the racism comes in, because the locals often saw black men with white women as being inherently immoral.
That said, there was a xenophobic aspect to the passage of the original act as well. In order to gin up the sort of public support you need for what is essentially "prohibition, but for sex" you need to play on something stronger than dudes' desire to get laid. And that, generally is the fear of "their women" being taken by a foreigner. The foreigner in question being mostly depicted as chinese, which is an interesting wrinkle.
So you have a law written up by puritans during a period when moral crusades were popular. In an attempt to ban prostitution in general by playing on anti-immigrant and xenophobic fears.
As to why a white woman might fear being arrested? Well the same reason any sex worker would be afraid of being arrested. The law criminalizes and punishes all participants. Which is of course ironic, considering the original purpose was to "save" women from vice. But that's pretty much the way of most laws against prostitution. At the end of the day, the puritans really care most about stopping people from having sex they disapprove of.