They are not in any way "impartial" on moral issues. I'd argue that they are by far and away the people who are most likely to be the opposite, given that religious people repeatedly contend that absolutely everyone should be obliged to live by their particular religion's dogma irrespective of whether they are an adherent of that religion or not.
As PP said, they are invariably and continually a drag on progress. You just need to look at what happens any time the debate on assisted dying rears it's head. Suddenly both houses are full of people citing religion as a reason to opt out and pass the buck, despite most of them never having displayed any overt religiosity previously.
Sorry Mr suddenly religious MP, your religion might give you one particular set of morals, but I don't share your religion, and neither do the majority of people in the UK either, and I disagree with your churches view on moral matters, so I'll be damned if I'm going to accept being subject to the whims of government by Theocracy just to avoid upsetting your God that I don't even accept exists.