Eyewitness accounts are evidence, my friend. You choose to discount the evidence because, presumably, you think these members of Congress are liars. I have no reason to believe they are liars and I find it entirely plausible that, given the fact that there are indeed racists among the tea bagger, racial epithets were shouted.
It's not that I must believe anything negative about the Tea Baggers, it's just that this particular incident is entirely believable. Take the spitting incident, I believe it was unintentional and more of a spray from yelling like a freak.