Jude's Letter

It's kind of chilly outside today, so I'm in the Mezz at Capital University.  Jude wrote this letter to let Christians know that although they're saved, the can't go around and do bad things.

Titus 1:5
I want to remind you that the Lord delivered his people out of Egypt, but later destroyed those who did not believe.

Titus 1:18-19
..."In the last times there will be scoffers who will follow their own ungodly desires.  These are the men who divide you, who follow mere natural instincts and do not have the Spirit."

Don't we all do that?  Don't we all follow ungodly desires?  I know I do.

What does it mean when it says "who follow mere natural instincts and do not have the Spirit?"  Does this mean we are to not follow what the body is to instinctively do?  Are not to "fight or flight?"  Are we to not follow our sexual desires, (which we shouldn't before marriage anyway)?  Are we to not feed ourselves whenever we're hungry?