The internet.
The internet allowed for the mass spreading of opinions, ideas and propaganda.
Social media, as said, was the ultimate way to portray a message.
Kids spend all day on it. Not always directly, but they will have a phone and will have an account.
All accounts get access to news stories they post.
All accounts get access to shit like buzzfeed and all that which is spammed.
Ideas are hammered into kids heads, and then an idea becomes popular with kids.
Then kids and teens will adopt this idea and say anyone who doesn't agree with them is outdated and bigoted.
People who don't feel that way will pretend to feel that way to avoid the label, and then older people will pretend to feel that way to pander to the younger people.
Soon, people who pretend to feel that way have their adopted opinions reinforced fiercely in the hyper-intense hugbox that is liberal propaganda, and suddenly you have a generation of people who believe they are the ones who know the truth.
They believe their truth is formed based on logic, fairness and intelligence. They think they have formed their own opinions, when really they merely all formed an opinion which adheres to what is required to not be an outcast.
"I don't mind black people, I just hate those damn ghetto ones!"
"I have no problem with gay people, not sure about trans people though!"
"I'd love a gay best friend! Ew, a lesbian?"
All of these opinions are eventually consumed and morphed into the idea that everything is okay and acceptable, except being white, straight and male.
They will all want to be smart. They all want to "prove" how smart and aware of the world they are, even it means attacking someone for being something that they are, whether it's straight, male, white, american, british, whatever.
If you disagree, you are a bigot.
If you half agree, you're an enabler and therefore a bigot.
It's one big, disgusting rolling stone that has gathered degenerate moss for years now.