It seems to me that when the goal is to ascertain a
person's beliefs, memberships in organizations
constitute perfectly relevant and useful information.

The "are you now or have you ever been..." question is
viewed as disreputable because (in many people's
opinion) it was asked on occasions when the beliefs
in question were nobody's business.

But once you've decided that someone's beliefs are fair
game for an inquiry, I don't see why you'd want to
exclude useful information from that inquiry.