"Man is the measure of all things" - Protagoras
A while back I said that I'd get around to explaining what the sophists got right. Well, here goes:
The Sophists were right in pointing out that beliefs are relative to the perception of man. (Ok, I'm being terse, but I'm not feeling so well at the moment. For more info check out the Internet Encylopedia of Philosophy entry I link to above.)
But recognizing this fact, we can attempt to employ objective methods of inquiry to overcome personal bias and increase our knowledge of the world. This is the aim and purpose of science.