This is it in a nutshell. It is bizarre that Bruce, the man obsessed with trust and dedication, has no qualms about hooking up with his friend's daughter.I'm regards to the captain America heel turn, I saw way more outrage the praise for that.
The issue I have with the batgirl /batman thing is that coupled with the age difference, Bruce is kinda screwing his best friend's daughter. That is kind of messed up.
The age difference might not even be that different in actuality, and they are both adults, but something about that relationship never felt right to me.
And this is coming from someone who thinks The Killing Joke is the most overrated Batman comic of all time (still fairly good, but overrated). I'm not terribly adamant that the comic be adapted in its purest form, but this addition does nothing to help.