There's one of two reasons to not feel guilt. Either you're body has a chemical imbalance, where you completely lack a conscience, or you are just blatantly burying the guilt that you feel to try to feel better about yourself. This is to those people who bury the guilt, bury it so far down that they think they are making themselves feel better about themselves for what they did to feel their guilt.
First of all, why? What is so easy about hiding that guilt? I want these people to realize it will hit them eventually. You may have trained yourself for years to not feel guilt, thinking you never have to apologize, thinking you are better than saying those words, "I'm sorry" and proving it, but eventually, deception catches up to us and that guilt will hit you.
Don't wait for that day. Recognize that guilt now and clear both your heart and head. One day something will happen to you where you wonder, "What did I do to deserve this?" and you will go through your past searching for the answer. When did you intentionally hurt someone, when did you lie, when did you not feel sorry for these actions, when did you not try to fix it? And that is when the guilt will come and you will do anything to try to finally fix it at that point, unfortunately, most times too late.
So don't wait for that day to come. You are given this emotion, along with others, to recognize them and act on them in positive ways, not to bury them to make yourself feel better for the time being. Face your guilt, fix what caused it, recognize your mistakes before you make the same ones over again.