I don't pretend to know too much about Free-Masonry (if there is such a word), but really why do people feel the need to stick their nose into other people's private lives? If it is run as a club, with rules and regulations, even a code of behaviour that everyone signs up to willingly, why should I care as long as everything they do is legal. I say legal and not 'above board' because why should it be open to everyone to see? I understand concerns over nest-feathering and the like, but are you really telling me that doesn't happen in other walks of life (old school tie and all that)?
If we start to get into the habit of making people declare their membership to Clubs, where will it end? There are people out there who would seriously cast doubt on a individual's suitability for a job if they found out they supported a certain football team (clearly Man Utd supporters could not get a job in Manchester...), and everyone has their own bias. Religion is a great example I won't get into!
Personally I found talking to a Mason mate of mine a really interesting experience, he was very selfless and it just seemed like an OK thing to do. Let them be and let us all look more closely at our own lives and see if we do as much for our brothers and sisters in the World.