I question your comparison of online sexism or racism to apartheid or the Berlin Wall. I try to stay away from comparing issues, but those were massive issues in which people died or were separated from their families for years not knowing if they'd be seen again. I can only be thankful that online sexism and racism are not as pervasive or life-changing as the aforementioned issues.
It would certainly explain why there hasn't been a change yet. But that doesn't change the facts: there will always be assholes on the Internet looking to get a rise out of someone, or people who blindly follow others in order to feel like they're belonging. If you see someone who's a moron, just be the bigger person and leave them alone. If you feed them, they multiply.
That's why the literature on the Internet agrees almost unanimously: don't feed the trolls. Don't even give them the time of day. It's not worth your time.
(just make sure you're not discounting legitimate opinions in the process)