I would like to point out that a game that's rated T for teens wasn't exactly created to make good role models for little girls. Granted, I do know that kids end up playing games rated T, but that's definitely not the target audience and thus the developers have no obligation to cater games to that demographic.
I do understand why people would claim that stuff that doesn't affect gameplay ruins the game. For that, I cite Metroid Other M, a game that would have gone down as a decent enough, if not up to high expectations set by previous titles, action shooter if it weren't for the atrocious story that glorifies abuse, badly handles bringing over stuff from the Metroid manga (like Samus's PTSD) to the point where its confusing at best and insulting at worst, and gives Samus and Adam characterization that spits in the face of Metroid Fusion (the game Other M is supposed to be a prequel to) and Metroid's contributions to feminism in gaming. The story and the lingering bad taste it left pretty much killed any enjoyment the game could have provided for fans, heck, it nearly killed the franchise. So its clear that gameplay isn't the only thing that makes a game fun. However, at the same time, its deeply concerning that homosexuality merely being present in some form is a fun-killer for people like the implications of abuse was for Other M, because there's really nothing wrong, sickening, or horrific about being gay.
The haters are definitely overreacting. Its a normal, loving, consensual relationship and should be treated as such. Tracer can still be your waifu in the realm on fanon, and you can still draw and look at porn and romantic fanfic of her with anybody of your choosing*. Besides, its not like you had any chance to hook up with a fictional character before she was revealed to be lesbian.
I will commend Blizzard for taking action against homophobic outbursts posted on its forum. Its swinging that banhammer all around to homophobes with a zero tolerance policy-- and its swinging fast. I will also commend the gamers that have condemned the hatred. The majority are in favor of this relationship or don't really care either way, and its not letting itself be drowned out by the homophobes. Good!
*Am aware that most Tracer porn and romantic fanfic has her be lesbian for Widowmaker. I wonder how many homophobes are connoisseurs of those...