Yes, this seems more likely. If you create a new website with first 10 toxic users, it will never grow, because they will scare away any potential 11th user.

Yes, this seems more likely. If you create a new website with first 10 toxic users, it will never grow, because they will scare away any potential 11th user. But if you create a new website with awesome users, it get useful content and grow. When it grows very large and attracts too many users, you will have to start moderating heavily. But moderating a website is an exhausting task, and awesome people usually have other things to do; so gradually the job will be taken by people hungry for some kind of power. Then the site becomes toxic.