Why does Roger Clemens have to answer Congress' questions?

If I was him, i would plead the 5th and tell them,... "I have done nothing wrong, but feel free to make a case and prove it in court if you think you can. As an american citizen, I am innocent until proven guilty. and by the way, gents...dont you have some serious problems to deal with like the ongoing economic meltdown and 2 wars?"