The answer is quite simple–gambling is bad, unless it leads to more money for government, in which case it is good.
Radly Balko of the Cato Institute also points out the the intention of Congress to pass these measure to demontrate the lack of corruption, in lieu of the Jack Abramoff scandal, is misguided:
The odd thing is, contrary to what the anti-gambling folks would have you believe, Abramoff didn’t want to legalize Internet gambling. He wanted to prohibit it–but in a way that carved out exceptions for his high-rolling clients. (Abramoff’s clients were a company that helped state lotteries sell tickets online, and the Indian casinos.) The various bills now under consideration are remarkably similar to the bill Jack Abramoff wanted passed.