I think this is a legitimate point. We have imperfect elections because we have imperfect people. Expecting a clearly unsaved person to act holy is the height of idiocy as well. We aren't electing a "pastor in chief" and we shouldn't expect anyone looking to higher office to be so. Frankly, I don't think anyone in a national office (Legislative and Executive branches) is free from corruption.
However, this isn't my issue with Mr Trump. He is, imho, a terrible candidate who is, as I've mentioned, no different than his future Democratic opponent. Between the two, I choose neither. This decision isn't based on his attempts at portraying a Christian witness or some moral standard he couldn't possibly achieve, but rather that he is a man who is more corrupt than any in recent memory, one with such bad ideas they actually make you want to run screaming back to English rule, and someone with such misogynistic, sexist language that I want nothing to do with this man leading our nation.
I just believe there is a candidate in the third party group that better represents my ideals and understanding of governance. That's where I'll be placing my vote in November.