I think that notion that having a sexuality that allows for both m an f pcs to romance a character makes them dolls is strange given then fact that there's very few times when the actions or race or appearance of a character has little to know influence. You can spend DA 2 killing all the mages and Anders will still romance you until you reach his crisis point in Act 3. Before then, it has no affect on whether or not you can be with him. Isn't that more odd than if he only would romance you if you were female? To me, it's far more jarring than having him be bi could ever be.
I already told that I consider DA2 romances to be flawed - straight or not. I also think that romancing a character which obviously diasgrees with you and almost hates you (or should hate) is weird, but nevertheless I liked DA2 romances. It's just that they could be a bit more thought-out.
I don't see how they are any more or less 'dolls to be romanced' if they are bi, straight or gay.
That's my whole point here. Characters may be bi, straight, gay or asexual, and there's nothing you can do with that. If you chose to play a gay male, don't be frustrated if straight characters won't engage in a romantic relationship with you. And vice versa, and so on.
On the other hand, when ALL romanceable characters are bi, for the sake of the player who doesn't want to change their favourite PC, I consider it to be pure "fanservice".