Why do Republicans oppose the financial reform bill?

Someone asked me that question today. Is it just the current political climate? Don’t shady practices interfere with the free market system? After all, the stock market has regulations to make sure it operates as it should. Why shouldn’t we regulate these other financial markets that, when they go wrong, mess up the entire economy? Are Republicans in the pocket of the big investment banks?

Could someone explain? (Don’t look at me to do it. This English major thinks “derivative” means non-original.)