Remember, any fish you don't keep is a cull. We just think of killing automatically when we hear cull.
I would always sell as many as you possibly can, which isn't too hard if you breed decent quality fish and sell/advertise on forums, facebook, locally, etc.
After at you can give them away (they can just pay shipping)... Same thing... Advertise.
I'm with GhostFeather... I don't think it's right to bring life into the world then destroy it because it doesn't look perfect. Deformed or other damaged fish are different... Depending on how serious it is those would be euthanized. Then again, it's a very personal decision.
To avoid getting into a situation where you have 100+ adult fish you can remove eggs from the nest right as you remove the female... At that point they aren't developed enough to feel anything.