Moral implications of heaven and hell doctrine Many Christians believe that when a person dies, they go to either heaven or hell. Catholics believe in purgatory, but most Protestants seem to not believe in this doctrine. Furthermore, the vast majority of Protestant Christians claim that salvation comes about through having the right belief in Jesus - who he was and a theological understanding of what he did.

http://en.wikipedia.org/wiki/Soteriology#Christianity

This doctrine of eternal consequences without the ability to get purified in purgatory never really made logical sense to me for a number of reasons, including the contradiction between Old Testament righteous people seeming to have a good afterlife without knowing about Jesus, and slippery-slope questions about children, mentally handicapped and others who simply never heard the gospel but were more or less good people. I have encountered at least some answers to these objections, although they seemed logically incoherent to me. However, I have not heard any answers at all to the following:

Let's suppose that the Christian dogma of heaven and hell is correct. That would mean that the ultimate moral consequences are determined by God. If a person cannot bring themselves to believe in "Mere Christianity" -- because, for example, every time they try to examine the evidence for/against Christianity it leads them to the conclusion that this is a man made legend and nothing really supernatural occurred -- what incentive or reason does this person have to behave morally at all? According to Protestant Christianity, no matter how good an unbeliever behaves, even the kindest old lady gets the same exact fate as Hitler and Pol Pot. Isn't this a reductio ad absurdum, showing that the heaven/hell doctrine provides for no moral incentives for unbelievers to act good without Christian belief?
The answer to your question "Isn't this a reductio ad absurdum, showing that the heaven/hell doctrine provides for no moral incentives for unbelievers to act good without Christian belief?" is (essentially) yes.

Christianity is more than doing good to others. That is the second commandment of the law. The first and greatest is to love God. (Matthew 22:36-40).

Hosea 6:6


  For I desired mercy, and not sacrifice; and the knowledge of God more than burnt offerings.


This may run contrary to your notion of "good", but be that as it may, Christianity holds faith in God as necessary to true goodness, or righteousness.

Hebrews 11:4


  By faith Abel offered unto God a more excellent sacrifice than Cain...


It wasn't because of his wisdom, charity, wit, etc. that Abel's offering was more excellent; it was because of his faith (in God).



That said, this statement is a bit leading to a Christian: "No matter how good an unbeliever behaves [he gets] the same exact fate."

The fallacy here, is the possibility people can be very "good" but choose to reject Jesus (and by extension, God himself).

All good comes from God. And therefore, good things acknowledge and worship God.

James 1:17


  Every good gift and every perfect gift is from above, and cometh down from the Father of lights, with whom is no variableness, neither shadow of turning.


Likewise, those who truly love and worship God are good.

John 4:19


  If someone says, "I love God," and hates his brother, he is a liar; for the one who does not love his brother whom he has seen, cannot love God whom he has not seen.




Now, it is important to remember than spoken belief (e.g. "I murder and have no remose, yet I believe in God") is not equivalent to true faith.

Matthew 7:22-23


  Many will say to me in that day, Lord, Lord, have we not prophesied in thy name? and in thy name have cast out devils? and in thy name done many wonderful works? And then will I profess unto them, I never knew you: depart from me, ye that work iniquity.




Thus, true faith in God and true goodness, according to Christian belief are not separable. Of course, not all are taught Jesus, or at least not fully. There are several questions about the fate of the ignorant. (1) (2)