Your beliefs are your concern, just please don't let them creep into our secular argument (idea)

What The Custodian is saying is that he/she/it is unwilling to conduct a debate if the other person brings in something to it to which The Custodian cannot personally relate.

You wot??

• "Your sense of humour is your concern, just please don't let it creep into our serious argument".
• "Your national identity is your concern, just please don't let it creep into our political argument".
• "Your sexuality is your concern, just please don't let it creep into our social argument".
• "Your experiences are your concern, just please don't let it creep into our personal argument".

People's belief are part of who they are - whether they be beliefs in God or in the equality of all men or the ultimate reasonablesness of science. If you can't talk to someone because their personal point of view differs greatly from your own, you're going to find yourself having narrower and narrower discussions.