Very often, you will hear someone say "I love you and I want the whole world to know about it, so I'll shout it from every mountain at the the top of the world" (they don't want there to be any doubt of who they love, actually it's just something that they have to say). If a person makes their love make sense, then it won't be true love anymore, love has to include some silliness and even be irrational.
Islam does contain factions (as any part of society). The Muslim people tend to be very gentle people except for those factions. Islam tends to be very cultural so that each culture likely has a different attitude about chopping off hands.
They themselves would also rationalize that their "reclusive" faith should not be scrutinized or verbally challenged by claiming privacy, cultural differences, or anything else they could think of, but I would think that the real reason is as you say,...outsiders worthy of being let in (racial purity), or is it just called "snobbery"?
Offhand, it would seem that Christianity is consistently exposed to more scrutiny than any other spiritual belief in the world. Sure Judaism keeps to themselves, but Judaism doesn't attack or belittle Christianity either.
I used to be a Catholic. Every human being can sense when something is really not rational (it simply doesn't make complete sense). If you read the article about Mother Theresa questioning what she was taught to believe as true (the woman herself probably could have WRITTEN the Sermon On The Mount) and loved The Lord immensely, but what she was taught (bureaucracy) didn't make sense to her (assuming the story is true,...she certainly did always put the Vatican to shame and maybe they want to discourage others from following in her footsteps). The Muslim people have come to accept and be obedient to their way of life, but how can a person truly make sense out of chopping hands off?
I couldn't help but take special notice of an advertisement I saw online because, traditionally, the Muslim people don't come from the most peaceful and free societies in the world, but now when they come to the U.S., they learn to smile (but I sure couldn't make sense that women should be covered up this way, 90 degree weather?).