No, not ban them from the civil service. Just have a register of interests or whatever. That way, if they were due to be involved in a decision making process, say involving anything to do with the RC Church, that would be known, and if thought appropriate, recuse themselves from it.
I think there is a case for a register of interests for senior civil servants and Judges.
I don't think I'd need to know if the guy taking payment for my car tax was in the Knights or the Masons. But a senior official in Education or Justice could wield a lot of power and it should be known if they have a conflict of interests.
If people are gay outside of work should that exclude them from any decisions relating to children ? or Maternity services ?
Or is this just targeting people who have a religious belief ?
The assumption is that because you are a member of an organisation or group or gender that you automatically do things in their favour which I believe is false. Some people do act like this but the majority do not.
The banning of people from being members of organisations starts with Religious organisations and then after a while just permeates to something else and then it becomes a specific requirement to be just part of one organisation to be considered for employment etc.
I believe in innocent until proven guilty. Until it is demonstrated that they are bringing it to work they're innocent. Whether they are members of an organisation or simply hold that organisations point of view what difference does it make? There are (or if not should be) mechanisms in place to deal with those who are seen to be operating outside their modus operandi. And if found to be in breach then throw them out