Didn't Paul murder Christians? Are we lookiing at Martin Luther as our savior? No, God uses sinful, bad people despite themselves. If you want to go on this tirade of "I can't beleive protestantism, because of who martin luther is" you make yourself his judge, and God will hold you to that standard. Calvin had a heritic killed, does that mean that we reject everything from him?
IF we held to that logic, then no one would ever be able to to tell anyone else anything based on thier misdeads. think about it