The assumption that the world would be a better place simply by virtue of the absence of religion is absolutely stupid. Imagine Spain exploring South America in the sixteenth century; is it really your position that if the conquistadors lacked religion, they would have been less violent? Give me a break. Last I checked, atheists were not immune to greed. The worst atrocities of the twentieth century were born from atheistic philosophies: communism, fascism and nazism all put non-religion at the center of the greatest good (the proletariat, the state and the race, respectively).
Again, I don't see your point about MLK. First off, I seriously doubt he would try to justify his affairs. Second even if he didn't, so what? It says nothing about religion - it only speaks to his character. No one would argue with a straight face that MLK's position on racial equality is invalid because he had an affair. How in the world, then, should any of his other beliefs be invalidated by employ of the same argument? Balderdash. That's right, I said it, BALDERDASH.
Trooper - We've had this conversation before. The only way I see homosexuals convincing the skeptical is by showing that homosexuals are normal people, not crazy blind hedonists (i.e. portrait of a gay pride parade attendee). In the end, I believe it will be far better for homosexuals if marital rights come out a legislative process (a la the post civil war amendments), not a judicial one.