Most of the hate comes from how much she's inserted into everything and people not being fans of her polyamorous status. If either one of those factors were gone, she wouldn't get so much hate.
I always treated Cait like Isabella from DA2. Its just their personality. Sure its not my thing, but to each their own. I don't really care sense I typically play as a white mage, so...Cait is banished to the inn. If you don't want to see her fucking everything you can avoid that content. Her having a lot of content, I always expected that since she is literally the first character you meet.
Also my character fucks everything with the exception of Demons, so who am I to talk.
I guess an additional criticism I'll make (which I'm sure other people have already made) just give people a choice.
Because Isabella in DA2 (to my knowledge) does not get the same hate, and I believe its because if you pursue her romantically in DA2 she goes monogamus for the most part. (She'll try and sleep with Zeveran but you can tell her no and she'll respect your feelings.) But, I would just chalk that up to Isabella having an actual personality and the devs considering that players may feel differently than them. God I love classic Bioware (even though I still consider DA2 6/10 game on its best days.)
Edit: Essentially the problem with Cait could be fixed by simply by giving players and actual say in a rpg game. I sometimes wonder if the devs know what the first two letters in rpg stand for. But, yeah I guess I agree with the criticism some people have made of Cait.