RE: why was davekat so disliked

a large part of it was that homestuck has built up some relationships for both characters only to tear them down later (big one: karezi), and a lot of fans felt like davekat was a "lackluster replacement" for those ships. part of the davekat hatred is rolled in with the general dislike of the retcon/ending, a lot of people believe that homestuck "was meant to have a different ending" or was underbaked at its end, and see davekat as a consequence of this "mistake".

really what happened is terezi and karkat's relationship had a lot of ship teasing and build up, and davekat never had any explicit flirting scenes or anything. that's kind of the whole point, davekat are just two dudes who like hanging out with each other which in reality is a way better foundation for a stable and healthy relationship than messy bickering of two thirteen year olds who don't know how to navigate a romance. really homestuck as a whole kind of makes the thematic statement that the best relationships are ones that happen in the background, are based in two people just kind of enjoying each other's company and whose romance doesn't exist for the reader's voyeuristic pleasure (like arasol, callieroxy for example...). a lot of people missed this point and thought davekat was just bad writing.

so most davekat hate really boils down to either hating the ending as a whole, or people who thought the straight relationships that were teased in the beginning were actually meant to be endgame and weren't there basically for the sole purpose of deconstructing them.