OldPaths

I think you answer your own question. It's associated with sin, lust, lack of self-control, pleasures the flesh and you can't see even on thing that God would find desireable in it.

We're to really subject the body to discipline. Not in any strange way, but to let the desires of the body lead our behaviours is not the best way forward. Food can be another place where we lack this self control and indulge the cravings of our belly. The Scriptures talk of those whose god is in their stomachs - and I think there is a fundamental sense in which masturbation often leads that 'god' a little futher south...

Guilt? If you're feeling guilty, it's a pretty sure indication that you've transgressed a moral rule you have for yourself. Your real course of action, then, is to determine whether the rule is based on God's will - or simply something you've constructed for yourself. If the former, then yeah - guilt is (often) a natural consequence of sin. If the latter, then it's up to you. If you're using the rule to help you live a more disciplined life, it can be a good thing. If you're using it to make yourself 'right with God', then you're basically being a Pharisee and rejecting the truth.

For what it's worth, my personal opinion is that it is very VERY difficult to engage in masturbation without sin - perhaps not in the act itself - but in all the deceptive and peripheral sins you mention that so often accompany the practice.