If people hate Joe Rogan for having anti-vaxxers on his show, does that mean we can hate Oprah since she had Trump on her show?

A better reason would be because she started the television careers of Dr. Phil and Dr. Oz, as well as regularly featuring all kinds of absolutely horrible bogus health information. Trump was already famous and good at self-promotion, he'd have been roughly the same with or without being on her show, but it's hard to estimate the amount of damage she caused by giving major boosts to medical frauds.