There will probably be a bunch of posts by the time I'm done, but anyway.
The save system discussion seems to come down to the in-game system of managing saves, since copying the save folder is already possible. In that sense, save restrictions seem to come down to the matter of realizing your desired method of play, the community schism argument, the game vision and how the game is supposed to play, and also bugs/the specs of your machine (which suggests allowing some customization). If I missed something let me know.
Due to current crash bugs, and how good saves have been at squashing them, I think an optional yearly or even seasonal autosave would be helpful for me. People with slower machines could turn it "off" to avoid the save time, or "on" to avoid the load time, as they like.
However, I want to understand the objections better as well. Options below are taken to mean various options, not just save options.
(1) If willpower is a problem, it seems like having an option to lock a world (is that what JT mentioned?) into a certain options set (most likely the main set or harder) would stop temptations from being an ever-present threat. This would be irreversible, but you'd know what you are getting into. If we made it reversible, then the willpower issue would arise again.
(2) I don't yet understand the argument about community schism. Is the argument that things such as the forums and wiki and so on would suffer from various styles of play? Is community shrinkage the proper response? Even with options, the game elements remain the same and the core game would not be watered down, given (1). Is the forum/wiki problem that serious? I don't think you'd suffer from a shortage of hard-option perm-death players around here. TT and I are, anyway. I might occasionally take a break to read a forum post about a small sandbox fortress, but I'd never make one unless I were testing a bug.
(3) I don't understand the argument about people not experiencing the full depth of the game, since they'd be aware of what they are missing to some extent, and many of them wouldn't play at all otherwise. Once a player leaves, what they miss of the full game is immaterial. That said, it should be clear (ASCII) that we're not watering down the game just to keep a larger audience. But adding a resistable easy-to-implement option to allow somebody to experience whatever piece they want of a game doesn't seem like an awful thing, at least given my lack of understanding of (2).
(4) As for game philosophy, we've never thought of this game as a roguelike in the sense of "death lessons", though it plays like that. Threetoe and I didn't play Hack 1.03 to learn the tricks necessary to survive. We just liked populating our high score list with the dead -- the worst mistake was to forget to name your killer if you had a high score, since it messed up the other colorful names in the list. In DF, you'll always be able to learn a lot from dying, and the world is enriched by it, so in that sense, your personal experience with the game independent of a community would not change.