Youtube is a world-wide technology and the videos can reach an impressively large percentage of the human population. No matter how good the average person is, there will always be some percentage of bad actors, and the larger the audience, the larger number of bad seeds there will be. Additionally, the nature of relevance algorithms and online social networks, amongst other factors, tends to silo like minded people into networks of similar content. And finally, there are a myriad other factors such as engagement metrics, relative anonymity, and plenty of other things that serve to provide encouragement and cover to comment and create content which would otherwise not be acceptable in most circles in person.

This means a video which draws attention of people with nazi tendencies as well as allied groups who are simply attention seeking can end up attracting a higher than normal percentage of those groups, and others from congruent social spaces. So long as there’s little to no impactful negative repercussions nor effective moderation of the rules, comment sections can fill with undesirable, despicable, illegal, and/or rule breaking replies.