A well written letter, not e-mail but letter to whatever the customer service address (especially if you ask to 'write a letter to the president/corporate office'. Not that the company president will get it but that's the folks that deal with escalated issues) will generally get you ten times the response of spamming a forum thread. Forums generally reflect the absolute worst aspect of your customer base, regardless of what business you are in. A written letter, especially an intelligent one, is more likely to generate a sincere response.
DA:O has same sex romance options as have a few other games. classical RPGs are more prone. As ME1 and ME2 especially were aimed more at the console shooter market but with a heavy RPG element it doesn't seem unreasonable that the backlash would have been worse. Enough to impact sales I have no doubt. Just look at these forums, skewed though they may be and add all of the soccer moms crying 'Not that I have anything against those, err, gays, I just don't want my dear little Timmy to play a game involving, err, homosexuals!' If Shepard was written as homosexual I suspect you wouldn't get all the same people here saying 'Well, It's BioWares game to write however they want!' They likely wouldn't have bought the game but would likely be screaming about it on any forum they could find, 'Why would BioWare do such a thing?!?'
BioWare isn't required to help move the social agenda along. Historically most advances in civil and human rights have been driven by the higher courts, not legislation. In the US the idea of racial equality was forced into place in the end by the supreme court. Legislation and the common public opinion wanted the Jim Crow laws. Public opinion did not support the idea of racial equality, neither did the legislative branch of the government.
All of which is neither here nor there. The truth is that given the opportunity, history shows that majority of human beings will be sucky to anyone they can identify as not just like themselves if opportunity permits. Businesses though are driven by majority and as such games like Mass Effect will not likely include M/M love interests. It would hurt their sales. That the truth of it sucks is another debate not suitable to this forum.