Since TJ used to be a critic, I don't consider explaining this especially off-topic.
Basically, there are two big reasons (other than being quite an abrasive guy) why TJ is disliked online. The first is that he insulted a rape victim on Reddit, telling her to "go drown in a pool of AIDs". Like I said, I enjoy TJ's content more than most people here seem to, but there's no justifying comments like that. I've searched around for another side to that story and can't seem to find one.
The second is that he appeared in a leaked sex tape where, among other things, he boiled his testicles in oil and shoved a banana up his arse. However, a big difference between this happening to TJ as opposed to someone in the SJW crowd is that rather than doubling down and trying to damage control, TJ admitted that it was him in the video and stood by it. He's even made jokes about it subsequently (including using it to own Onision), but there's no denying he's into some fucked up stuff.