This happens to me and fighting games a lot as I usually main slow, bulky brawlers like Tager and Potemkin. Only difference being I eventually get tired of them. My friends are always supportive of me trying new chars, they usually will too when I do it unless I ask for them to use their main. People online however...
Though instead of hatemail from people, I got one guy actually apologizing.
I've gone from mainly using Tager to trying to learn Tsubaki as I can seem to combo better with her. Got beat by a Hazama who sent me a message saying "I hit you with throwing knives three times, I don't know how I did that, I'm sorry. Good game." Was a damned close match though.
My advice Kon, if it's a fighting game give them hints or info on how to counter your character. Alternatively dumb down how you play a little or start learning another character you like just to appease them, and if you get "too good" with that one ask if they want you to use the other one.
I did that at a tournament to a Valk player after I had lost to a Mu to stay in the tournament. Felt bad afterwards when he said he was playing for fun.