Well, here's my take: There's no better time to learn an (admittedly somewhat Darwinian) lesson about caution, tactics, and just plain dumb luck - all of which play a part in character lifespan in D&D - than at first level. Better early in the game then once they've hacked their way up to mid-level and have a lot of time and energy invested in their character. (This is especially true in pre-3rd edition games, where it takes a
hell of a lot longer to advance.) And if you don't start letting the dice fall where they may at the beginning, you really can't go back - unless you're prepared to risk an unexpected TPK halfway through a campaign, just because you suddenly started playing for keeps.
I had a player (by no means a newbie, but one returning to the game after many years) roll up a monk in my current campaign. The monk tends to be a character that looks a lot more indestructible on paper than in actual play, and I repeatedly reminded him that he wouldn't be a front-line fighter until much later in the game, but in probably the third combat he was involved in, he charged ahead of the party to Layeth the Smacketh Down on some bandits, only to have the rest of the party knocked out with a
sleep spell from a hidden wizard. Two Ftr2s + one critical ='ed one monk at -9, and the deus ex machina clot check was not forthcoming...
He was bummed, to be sure, but it was bound to happen eventually the way he was running his character. I gave him the option to just create "brother of Monk A", with the same stats, but he chose instead to roll up a ranger that he's still playing today. What's more, he now plays a monk in a campaign we both play in, and he's much more cautious in battle with that character. In other words, lesson learned.
And, there's one other thing - You need to foster a player group that can handle it when things don't go their way. True - you may lose a player. There's not really a way around that, but if they can't get down with losing a character at 1st level, what makes you think they're gonna handle it better when they're 5th level? This is simply not a game for everyone, and some folks can't enjoy a game with no "save" feature.

Such is life.