Yes, it's quite easy to decieve yourself into thinking you are normal and the thought that you know you shouldn't do something quickly turns into thinking you feel as you shouldn't do something. Afterall, what do you have to compare the experienece to if you never truly felt guilt?

Some don't even realise it and some, like you said, know but don't care. Why would they? Does a blind man care that the sky is blue? The colour of the sky has never affected him in any way, shape or form and never will.

Dr. Robert used that colorblind analogy in one of his ask dr. robert pages called,

Can a Psychopath Be Taught Values and Morals?

He even posted some colorblind eye charts.