I think there are just generally too many of them around. It's bad for performance, they get in the way, and often I'll encounter a level 1 champion in the late game that I just don't want. Even if it's a light advantage I just don't want the macro. I'd like a system where the higher level ones didn't spawn until later in the game and unclaimed lower level ones disappeared after a while.

I would have no use for it, but I don't see why others who want it couldn't select it as an option--provided, as was suggested, that some logical form of penalty was attached to attacking one naturally allied to your side.

Sounds like a reasonable request. If you know you don't want them then the only alternative currently is letting the enemy (anyone else) have them. Makes sense for a third option to be added, such as "Assassinate", which could added besides Recruit and Rename and would take you to the tactical battle mode.
I don't see the need for a penalty unless you would get increased penalties in diplomacy from killing heroes from the opposite faction in addition to the ones already in place.

If only they knew the fate in store for them...  And with Steal Soul (like other strategic spells), you don't even need to be next to the hero.  They agree to help you for nothing, so you repay them by stealing their souls.

I tried playing betrayers + free recruitment but I decided that because of the way EXP is split its not worth hiring all those champions. The 1 gildar wages are too burdensome. It would have been nice if I could kill all the heroes that didn't appeal to me so I could get extra experience. I wouldn't mind if its a betrayers only trait... it makes sense : D.