The concern is surely that the possibility is that mainstream religious views might, and that's another word doing the heavy lifting of considering there might be a problem rather than just dismissing it completely, lead to it being impossible for people to be candidates?
Yet more speculation. And frankly I am (and I suspect political parties are) interested in the views of individuals - whether, or not those view may represent
'mainstream religious views' (which of itself is highly subjective) appears irrelevant. Not least because there are plenty of religious individuals who do not agree with the
'mainstream religious views' of the religions that they affiliate to.
So if a political party strongly supports, as a matter of official policy, the right for women to access abortion services, then it would seem perfectly reasonable to me for that party not to choose to endorse a candidate who wants to campaign for a complete ban on abortion. But that would be based on the individual view of that individual person - that this view might be
'mainstream religious views' in the RCC seems completely irrelevant to me.
Broad churches allow for different views, you seem happy for that to he reduced.
But I don't accept that political parties are less of a broad church now than they were, say 40 years ago. Indeed in many respects they are far broader - back in the 80s it would be pretty difficult to be endorsed as a candidate if you were openly gay, or openly atheist, or muslim - indeed it was pretty difficult to get an endorsement as a candidate if you were a woman.
And sure there are some 'views' that would appear beyond the pale now, that would have been OK 40 years ago (e.g. racist, sexist, homophobic etc), but there are also 'view' which now would seem pretty mainstream now in the LibDems, but would likely have been considered extreme and not been welcome in the Liberal party of 40 years ago - e.g. support for same sex marriages, lot's of views on green issues, support for assisted dying, support for smoking bans.
Times change and the fulcrum of views changes also - that doesn't mean that political parties are any less 'broad churches' it is just that the range of views considered 'reasonable' has shifted.