Left wing Do-gooders who believe that any diversion from their infantile world view should be countered not with reasoned debate or compromise, but with ad hominen attacks. Typically they silence discussion with epithets such as "racist", "sexist" or "homophobe" because they know that they would not survive long in a fair debate using Facts and Logic.
In the UK in the nineties, the rise in cases of HIV was mainly due to African immigrants diagnosed once they had arrived. Doctors tried to bring this to the attention of the health authorities but were called racist by the PC Brigade and forced to spin the story that it was due to unsafe sex by promiscuous britons, so failing to tackle the problem.
Usually some geek with an inflated ego and inferiority complex, trying to prove their intellectual worth to complete strangers, whom they'll never meet, on the internet. Will often illogically accuse you of logical inconsistencies/fallacies in your arguments, or just resort to picking apart a slight typographical/grammatical error, to give themselves an inflated sense of self worth. While the majority of YouTubers are annoying asses like this, sitting on the sidelines reading page after page of two YouTubers going at each others' throats like a pack of savage dogs can be of greater entertainment value than the video above.
If you want an example of a typical YouTuber, just hop on over to YouTube, click on almost any video and read the comments below. Enjoy.