Trusting in Reality

The moral relativist claims that we can know nothing on our own. My question for him, beyond, 'Then how can you know that?', is, 'Why don't you want to trust your senses?'

Why not trust them? Sure, they can be fooled, but can the tomfoolery not be discovered by clear thought, a presentation of the valid evidence, or exposure of the true villain, among other remedies? By and large, hot is hot, hard is hard, and mathematical progression continues uninterrupted by what we might wish. Why won't you believe your eyes, ears, nose, and touch, your own rational thoughts indeed, as need be?

The only reason I can think of is that any valid thought might interfere with what you might want, and we can't have objectivity ruin a night on the town, can we, brother? For you see, a proven truth in one area necessarily suggests there are provable truths elsewhere, including perhaps those which may affect how you want to behave. That simply destroys any moral chance of, well, doing an awful lot of immoral things.

Such a shame that human beings have to consider the weight of their actions to be fully human.