I believe, for example, that fighting is wrong. I don't feel good when I hurt people, even in self defense, and so I will try very hard not to get into physical fights. Sometimes I make the hypothesis that I feel so strongly against fighting that despite a 'valid' reason in terms of my personal morality (ie helping a friend), I'll still feel like crap after.

A lot of other people fight. There are lots of people who fight for sport. That, to me, is the dynamic opposite of what I personally believe in. However I don't feel morally outraged. In fact I will probably watch people fight. Then again this might not be a fair comparison because sport fighting != self defense fighting or aggressive assault fighting.

The point however, is that there should be moral 'truths' you believe in that aren't so important as to be objectively true, for all intents and purposes. I'm a subjectivist (moral), so virtually everything I believe in is just something I believe in. If however you think objective truths exists (moral truths), you have to give a rational basis for it. "Because I think so" is not a good enough reason because I could "think" the opposite and we can't both be right. "Because I (Roto13) think so" is equally pointless, unless you can illustrate why you are the sovereign ruler of what is moral.

Incidentally, even if God were to exist, it wouldn't be the case that just because God decreed something, it would be moral.