The Larry Craig non-news has an interesting undercurrent: people seem upset that he acts like a closet gay, however he also votes against allowing gay marriage (ignoring the quibble that he could be for 'gay lifestyle without any marriage idiocy'). More generally, should we feel outrage when a politician votes against their conscience?
On one hand, voting one's conscience means voting according to what seems right. On the other, voting against one's conscience implies voting based on something else (like consecutive term count maximization or what's best for the constituents). So, it seems that people prefer the demon they know (assuming the representative has average morals) versus the new demon of an unknown metric.
This tendency to assume that others share our morals probably comes from an earlier time when we saw everyone we knew every day. Their actions and thoughts were known, with the morally questionable ones being discussed. This social approval or disapproval probably kept people in line with their peers. However, we currently don't really know our representatives any more than what the news tells us.
Say that we accept that our politicians may have weird morals. We should then want to know why they make certain choices. So, the politician should then explain their choices as best they can. If we understand their decisions and they make sense, should we continue to trust them?
At the heart, this seems like a principal-agent problem, where we try to predict the future decision path of a representative. We can solve this trivially by assuming a working social moral exchange and voting for the person most like us (using genetic hints if we're operating on ancient assumptions). Any other choice involves studying prior decisions and making an educated guess.
We probably feel outrage as part of us trying to socially recondition the transgressor. The cynic would say that it's easier to be angry at someone we'll never meet than to admit that our naive voting algorithm created this problem.