The only way I would cull is if it would be almost impossible for them to thrive. I had to cull my first clutch because they were train wrecks. Some didn't have eyes, all their bellies were split a good 3-4 inches, and they had severe kinks. Their clutch mates were dying throughout incubation, but three of them lived long enough for me to pull them out of the eggs and they could barely move. This is the reason I go substrateless now and will never go back. I personally think it's wrong to cull any animal that can and will thrive. There is a difference between living and thriving in my book.