Kaidan is not heterosexual. He is a romance option for both femShep and maleShep in ME3, so he is bisexual or pansexual, or panromantic demisexual as the op says.
Bisexual and pansexual representation in media is already very limited, especially in video games. There is no reason to erase the few examples we have. I’m not saying you’re “a homophobic monster”, but heterosexual characters are literally everywhere. One less doesn’t hurt anyone, quite the contrary. It adds representation where it is most needed.