Many former Christians did not conduct their practice of faith any differently to current Christians. However, given that trauma often factors into why people began questioning and ultimately leaving their former faith, it is (and I can't really put it any less bluntly than this) profoundly shitty to go around trying to claim that a former believer 'was never Christian' or 'was never a true Christian'.

Most of us tried as hard as those we saw around us, and for a poster here to pretend people who are suffering from religious trauma were really just insincere or faking it or wrong but with no provision of how we were 'doing it wrong' in a consistent, discernable way from current Christians should be taken as seriously as e.g. calling a current Christian a fake Christian or not a true Christian.

For many of us, this is just insult to injury after the church screwed us over in the first place.

If this rule is already being enforced in this way, then fair enough, but I can't say I've seen it happen here much.