Ooh, philosophical this morning! But, this is an interesting question and I am just as guilty of it as anyone. Why do we continue to eat stuff we know will cause us more harm than good?
There can be lots of complex reasons – and believe me I have seen and heard a lot of them, especially having a clinical hypnotherapist as my partner!
I thought this post from Mark (author of the Primal Blueprint books I recommend here) has a good take on it. He explains how cravings for certain foods may actually belie certain primal needs. I agree with the principle; think of pregnant women wanting coal (need iron) or toddlers eating dirt (hygiene hypothesis, needing worms and bacteria) etc. We are a product of our evolution. We TGF-ers even more so; we cannot tolerate the ‘new’ agricultural foods.
Have a read anyway, it may help you understand, as he describes it: ‘what is going on under the hood’ (or bonnet anyway for UK readers).
Hope it helps. Don’t give yourself a hard time; you are, after all, only human!