Posts are in reverse chronological order.
Is man as bad as he can be? It seems to me the answer is a crystal clear: yes and no.
Yes we are totally depraved-- as described in the book of Romans:
as it is written, "THERE IS NONE RIGHTEOUS, NOT EVEN ONE; THERE IS NONE WHO UNDERSTANDS, THERE IS NONE WHO SEEKS FOR GOD; ALL HAVE TURNED ASIDE, TOGETHER THEY HAVE BECOME USELESS; THERE IS NONE WHO DOES GOOD,THERE IS NOT EVEN ONE." (Rom 3 10:12, NASB)
Left on our own we cannot do anything good; anything that is pleasing to God. We Calvinists take this to its logical (at least for us) conclusion: we cannot turn to God on our own, even just to accept his offer, for surely such an acceptance would be good. You don’t have to go this far to acknowledge that, apart from God, man is morally bankrupt.
On the other hand, man is not as bad as he could be. Even the worst monsters: Hitler, Stalin, Mao, Pol Pot, hard as it may seem, could have murdered more. As the humanists like to point out, most people appear, in terms of their outwardly day-to-day behavior, to be good. Indeed, the world around us abounds in Good Samaritans. In terms of “doing nice things”, it is hard to see a huge quantitative difference between believers and the world. (Unlike many who comment on this, I don’t find it shameful. What is shameful is the flip side: that the statistics for some “bad” behavior, especially divorce, are not substantively different.)
The answer to this is what is described in the concept of Common Grace. God gives to all men a measure of restraint. I don’t know all the reasons, but presumably one of them is to prevent us from self-destructing as a species. Here is where we disagree with the humanists: man is not intrinsically good, forced into evil by genetics or the environment. Man is intrinsically bad with wholesale degradation avoided only by God's grace.
God’s removal of this restraint, either gradually or dramatically, is the frightening process of having one’s heart hardened, the most famous biblical example being that of Pharaoh. However, anyone holding onto a particular sin, refusing to repent and seek divine assistance in combating it, also runs the terrible risk of having his heart hardened:
Therefore God gave them over in the lusts of their hearts to impurity, so that their bodies would be dishonored among them. (Rom 1:14, NASB)
God is not the author of sin. For his divine purposes he does at times withdraw his restraining influence in a person, revealing more of man’s truly fallen state. The dire consequences are entirely man’s fault, not God’s.