Some people think that in order to lead a morally decent life one may sometimes have to forego the possibility of having a good life oneself. Even if that is true, it does not render morality incredible, but it does raise a question about morality's authority: about what one has most reason to do when one is faced with a conflict of this kind.
Our actual lives, including our values, our social relations, our self-conceptions, and many of our concepts, are pervasively shaped both by the knowledge and by the fact that we will someday die - that we are subject to extreme temporal scarcity. There is no reason to think that, if we were immortal, the same things would continue to matter to us. We have little or no idea what, if anything, would matter to immortal beings, or even how such beings would think of themselves.
Tolerance is an essential value in the modern world, and we have daily reminders of how awful the alternatives to it are. And despite its paradoxical flavor, there are many good arguments - moral, prudential, and epistemic - in favor of tolerance, and none that I know of against it.
We are all seeking to live up to normative standards that we recognize, even if we don't all recognize the same standards. This is something basic that we have in common despite our differences.
Philosophical questions and modes of thought just seem natural to me. They mesh with the way my mind works.
