There are two kinds of sincerely religious people: the crazy ones and the sane ones. We've all observed the former (Fred Phelps & co., Mormons, and now, those people who sold all their possessions for the rapture that's been postponed); the latter are, depending upon whom you ask, perhaps only a theoretical possibility. (If pressed, I'd say I've probably met a few. But they draw far less attention to themselves than the crazy sort do.)
What is one to make of the sincerely deluded? Well, the first thing to emphasize is that they're usually not bad people (with the probable exception of that horrible Phelps clan): they are merely carrying a (nonsensical) belief to its logical conclusion. If I truly believed God was planning to save only 144,000 special folks, why wouldn't I knock on your door to let you know about it (and, if you were out, leave some pamphlets)? The fact that it's an objectively asinine thing to do should not concern me, should it? Your salvation is at stake!
Several years ago I passed a church sign that read, "Friends don't let friends go to Hell". (Yes, it was one of those churches. On a later occasion, the sign read "Pray first, then vote". They must not've had enough letters to spell "Republican".) In all ages of the world this sentiment has been true; all ages, that is, except our present one. Only now is it widely considered a virtue to tolerate heterodoxy among one's friends. (This is assuming, of course, that one believes in an ortho-doxy to begin with.) Is this a positive development? I daresay in many ways it is. I certainly have no desire to befriend the sort of Christian — generally one of the more foaming-at-the-mouth sorts of Protestants — who would endeavor to convert me to whatever obscure non-creedal sect he belonged to.
And yet at the same time this development probably says something about our friendships. It's worth noting that the medievals had a stronger sense of friendship than we do today. The Cistercian Aelred of Rievaulx (1110-1167) considered friendship a gift from God, a point upon which even the most deracinated Episcopalian or Unitarian can probably agree. But Aelred goes further: in true friendship, as in marriage, Christ himself is present as a third person. (I would give you a full quotation, but my library, which includes Aelred's Spiritual Friendship, has gone before me into Iowa.) Is this possible in friendships between two people of different beliefs? That is to say, if friendship is such a deep spiritual connection, to what extent are friendships between people of differing beliefs the real thing? I'm not prepared to answer this question. If Aelred is right, though, I should probably be prepared to admit that I've never truly experienced "spiritual friendship", for so many of my dearest friends indeed do not share my deepest beliefs. For some reason, though, I feel no need to start proselytizing.