Although YouTube may more content that's aggressive, it has much more variety of content(educational videos, news, etc.), same way why they wouldn't ban search engines just because their variety can include aggressive results, and because it is backed by a huge company. YouTube is so big, when countries ban or hinder its experience, news companies pick it up as a story. That's how much of a say it has in todays society.
Newgrounds is usually banned from schools and other public places because it's strictly a site for entertainment purposes which offers explicit content.