9For, doing this, thou shalt heap coals of fire upon his head.  21Be not overcome by evil, but overcome evil by good.

Do you think there is a bit of appeal to ones desire for vengeance in that last part?
And what about the notion of "Overcoming", as if you are to conquer their stubborn will with subversive tactics of being "Good" to them. Does that not make the charity false... if you intend to conquer and overcome and rise over them?
It is the same as putting a label on yourself "Good" and your enemies as "Bad", but the battle between you two remains.
As does the desire for retribution and to conquer.

And how does that compare with the Catholic virtue of being permissive when enduring opposition and not defending yourself.
Does this stuff work in reality, or is it camoflage for a hatred that never disappears but is only wrapped in religious self righteousness?

Sometimes it works.  Sometimes it doesn't.  

It is really hard to be kind to be people who are mean.  It isn't easy.  

Arguing doesn't work all the time either.   Maybe being ostracized isn't so bad afterall.  

I sometimes think that last poster (1st response to your post) is... in need of exorcizing... just being honest, not being snarky..