I mean imagine that you are playing as evil character and good character changes to the evil side (this is the reverse example). I've never seen this before... It's not fair that ppl always trying change evil characters, but this never happens with good characters.
It does happen, Kotor 2 and Jade empire come to mind from the top of my head, I'm sure there was more.
SWTOR does too, but only on The Empire side base class stories. I'm seeing a pattern. BioWare abandonned the concept now thought. Good NPCs won't mind your evil PC that much and evil characters won't mind your goody-two-shoes PC, the clinching is just faction based. And it feels so weird to romance Lana in SWTOR on anything but a Sith/Imp (or Dark Sided Jedi) to me.
The option to "fix" the evil romanceable NPC is much more common and send the wrong message I think (you are manipulating people just so they love you).
