I agree with the sentiment, but the nature of criticism is also more complicated than that. For example, take the criticism of the homophobia, toxic masculinity or misogyny in Snyder's films.
When people make these types of criticisms of other movies, most people would probably agree that they are, atleast a little bit, making a commentary on the personal views of the directors of those films themselves. I mean, how else does such an element enter a story if not at the allowance of the person controlling the film? And if that's true, then we have to ask why a director would allow such a thing. It's not always "If the director allowed this element of racism, then they must be consciously racist" because sometimes it's either something they didn't intend or understand and sometimes it's us having a peak into a darker side of the person making it. It's a normal way of interpreting any movie and it's okay for fans to use it as a lens to read any director - We all live in bigoted cultures and that bigotry has influenced our way of thinking about marginalized groups, so it is worthwhile to scrutinize how directors depict marginalized groups.
But every time I've seen that approach taken to Snyder and analyzing where he failed in regards to those elements, people who are fans don't take it as literary criticism but as an personal attack on Snyder himself. And, granted, you can't say it's an entirely impersonal criticism to make. If you're saying Snyder's films ennoble toxic masculinity, it's hard to argue your not also implying that Snyder himself thinks toxic masculinity is noble. And while not impossible, it's certainly difficult to imagine how a person who doesn't idealize toxic masculinity would create the kind of scenes he does.
I've said multiple times now how I think the multiple drive bys of "snyder sux" are, if not out of line, then certainly worthless as commentary. That is just nothing but whining and I'd rather it stop. But we also can't pretend that all criticism is going to be compartmentalized solely to the movies when no other criticism of any other movie works this way. At some point, you're going to say "The director included this element presumably because they believe in this", because it's impossible to make a piece of art without putting a piece of yourself in it. (for the record, I am pro-death of the author and try to eliminate author's weight on my interpretations where possible, and even I argue it cannot be done completely. And that's just me, other people who do like to tie creators intentions to their works don't feel the need to put distance between authors and their work at all).
So....yes, genuine personal attacks aren't good and I'm as sick of the "bitch is eating crackers" trend as anyone, but fans have to understand that if a person can actually elucidate their criticisms in a meaningful way, attacking Snyder himself can be fair game. And if Snyder is getting attacked that frequently, it may be at least partially because there are just that many problems with his movies.