Personally, its not that people hate Geno, but rather the "fans" (and I would say most of those "fans" are "bandwagoners", not legitimate fans of the character and/or the game he is from). They want the the thrill of tribalism and that high of "winning". If you point towards GameFAQs as an example of Geno being hated, the fact is that place basically hates any character that is popularly requested at all (they seem to be big contrarians in general).
"Bandwagoners" act the same regardless of any fanbase they are in. They gravitate towards any character with a high probability of getting in and a "high stakes and drama" around, and they will go out of the way to attack anyone who does not think highly of their bandwagoned character of choice. And when the character ends up being deconfirmed, they all forget that they ever supported the character to begin with (they did this with Ridley and Chrom during Smash 4), or even join in the detractors in making fun of that character.
You are a real fan. Use your clout to try to get the bandwagoners to act better (I know I tried to use my seniority as perhaps the original Ridley supporter to get them from believing those dumb shadow theories but to no avail).
Myself personally, I am a very big fan of Super Mario RPG, and it was my first RPG ever. It is still one of my favorite games for the SNES. However, my nostalgia and attachment with the game is not with Geno, but various other things with it (heck, Mario himself is very memorable and charming in that game to me).
I think you will get your single most wanted character next year (unless Geno ends up being at the end of the post-pass DLC), so take solace in that.