I honestly have no hatred toward any character's inclusion, even if I don't care for them in their source game or even in SSB (see: Olimar). I am happy to acknowledge that a character I may dislike is someone else's exact cup of tea and I therefore am happy to see them in the game.
However, every rule has an exception. For me, I loathe Dr. Mario. "I hate him so much, fla-- flames-- flames on the side of my face, heaving, breathless, heaving breasts, heaving--" (a humongous cookie to anyone who gets that quote, like for reals, I will love you forever). I really don't understand my hatred for him, but I just think he's the absolute dumbest inclusion, and the current leak with him in it makes me cringe.
The only thing I can do to make me accept him is to come up with some ridiculous head cannon for him involving him being either an alternate timeline "Doctor" version of Mario, or else an imposter who is like a Dr. Moreau come to Smash Bros to conduct hideous experiments on the participants and must be eliminated with extreme prejudice.
(Disclaimer: If you genuinely like Dr. Mario, please don't take offense at my commentary. I am happy for you, and I wouldn't wish for the Doc to me absent just for my selfish preferences. ^__^)