Then, by all means, please show the class the natural law, constant, or substance from which we can derive or observe objective morality.

Or, you know, don't, and just call me evil and pat yourself on the back because, goddamn, did you tell me, and isn't it obvious, you definitely know it when you see it, and what sort of terrible person would ever approve of things that give you the bad ick feeling, they must be evil. Besides, god told me this was good when he passed his commands down to a group of illiterate goat fuckers a few thousand years ago, and made them promise really hard not to forget or change any of his rules, which conveniently involved a lot of things that were moderately useful for groups of illiterate goat fuckers and didn't really include silly things like arithmetic, germ theory, or electricity, because that would be silly.