First of all, you can't turn on automatic syncing by "accident", you just weren't paying any attention to what you were doing.
As for having that warning...oh hell no. That type of warning is definitely a Windows thing and annoys 99% of the users.
I will choose not to take your comments as a veiled insult. I certainly was paying attention to what I was doing, I just didn't expect the results that followed. The specific dialog in question offers three settings: "Automatically update all songs and playlists", "Manually manage songs and playlists", and "Automatically update selected playlists only:" (with a list of playlists to checkbox).
I had it set to manual. Then I decided it might be nice if I could manually manage the songs, but have playlists update -- for example, I would really have liked to have the "Top 25" playlist update itself (which it doesn't do in the manual setting). So I revisited those three options.
When I choose "Automatically update selected playlists only", and select exactly one playlist (Top 25 Most Played), and click "OK", the one thing I do NOT expect iTunes to do is delete all the songs from my iPod. There was no warning, no confirmation, no bubble help or tooltips, the only thing that gave me a sinking feeling was the sudden flurry of hard disk activity on my iPod, which soon became empty.
You imply that confirmation dialogs are a Windows-ism. But, name me one other place in the Mac experience where the default action is to let you destroy that much data in a single click, with no possibility of undo, and no confirmation. The Finder warns when you empty the trash. So do iMovie and iPhoto. iSync gives you a chance to review mass changes before you apply them.
Whether or not the sync-songs-when-I-only-told-you-to-sync-playlists thing was a feature or a bug, a simple "Are you sure?" would have made it abundantly clear that this feature did not do what I thought it would, and would have saved me a big headache. You claim it would be annoying, but I see it as a safety net, and certainly consistent with the Mac experience.