It’s not about assuming the worst, it’s more about being skeptical toward anonymous people on the Internet you don’t know, which I think is healthy.
The problem with JP is that even if you agree with one of his positions, he has almost certainly arrived to that opinion through his other terrible assumptions. By sharing his take, you’re not just sharing the opinion you happen to agree with, you’re sharing the underlying worldview he uses to justify it.
If you really do care about people assuming your support for him, you should use your own supporting arguments for the opinion you’re sharing instead of shoehorning his in.