"He allowed it". No. He tried to balance the interests of running a business that was dependent on advertising for revenue, creating an environment where people would actually engage with the platform, rather than being harassed and dogpiled, and a bunch of poorly-adjusted edgelords flipped the table over their rights to be total assholes. And yes, mistakes were made. And in the end, Jack came to believe this just wasn't something a company should be responsible for. That's it. That's the whole story.