The problem is heteronormativity and exclusion. If you're going to include romance, only including heterosexual romance can easily make LGBT people feel very left out. You can say "it's just a game", but when this sort of thing happens to you in some form every single day (heterosexual people tend not to notice how heteronormative they are), it can have a huge effect. Straight people don't generally understand that, but might be able to understand these perspectives:
- A friend's family throws them a surprise birthday party but doesn't invite you because of the color of your skin
- A financially successful friend says you should buy the new expensive thing that just came out as if it's as simple as adding milk to the grocery list, not acknowledging that you're living paycheck-to-paycheck
- A friend gushes about the awesome time they had with their dad on father's day and asks what you did with your dad, but your dad is gone from your life (died, ran off, etc) or he's an abusive/neglectful person or you have two moms instead
One or two occurrences can be shrugged off but imagine any of the above happening to you every day. Imagine having to defend yourself every day against people who can't wrap their minds around you being the way you are. Imagine having to physically defend yourself because people think it's hilarious to "smear the queer". Continuously being told that being gay is wrong, either explicitly or implicitly (via heteronormativity), is psychologically damaging.
To you, this may just be about adding more sexuality to a video game. To many other people, it's about acceptance. It's about letting gay people have the same experiences in the game that straight people get. This is a really big deal.
With all that said, we've definitely seen in this thread several examples of "lesbian good, gay male bad" and I have no doubt that many of those people are indeed men that just want their voyeuristic fantasies represented in pixel form. However, taking everything I've just said into account, blanketing that over everyone that wants SGR is pretty insulting.