It can feel as though it weakens the characters. Let's say I am a Dragon Age fan who doesn't follow the Developer tweets and plays DA2. On my first playthrough Anders never mentions that he was in a relationship with Karl because I playing a female Hawke, so I assume he is straight and never had a relationship with Karl, but on my second playthrough I play a male Hawke and Anders now mentions a past relationship with Karl.
I want to write a Dragon age fanfiction about Anders set before the events of dragon Age 2, but do I write him as in a relationship with Karl or not? I have no idea because Hawke is not defined yet, and therefore neither is Anders. That entire part of his history, from my perspective having only played the games, relies entirely on Hawkes existence to define it, and therefore technically does not exist without them.
And aside from that there's just something about changing aspects of the characters that should be defined at birth as soon as the player character pops into existence that bothers me. If Bioware wanted wanted to they could let us could play in parallel universes where Isabela or Vivienne happen to be white, Varric is an elf or Anders isn't a mage, based on what we choose in character select. But I don't particularly want to play in a setting where the characters's persons change like that behind the scenes before the game even begins.
I agree that changing a character's sexuality based on the PC's gender is the wrong way to go. I agree with you 100%. I also want to say that I'm not really convinced that we've ever even seen a true player sexual character in a DA game.
However, my earlier point was trying to figure out the difference between these scenarios:
A.) I play as a female Warden and I "befriend" (maxed relationship) Morrigan. She has no dialogue that would indicate to me that she is available as a LI for a male Warden, and I never know because i have never played as a male Warden.
and
B.) I play as a female Hawke and I romance Fenris. He has no dialogue that would indicate to me that he is available as a LI for a male Hawke and I never know because I have never played as a male Hawke.
Why is one okay but the other is not? I don't see the difference here. I really don't. Again, I'm not in favor of playersexuality. My main argument is that DA 2 was fine (not the best, but fine) because, to me, these examples were both fine and neither necessarily is playersexual.