Joybell - I have Absolutely no problem with this sor of song. It is just proof that Time Travel is more common than the daily papers would have us believe. Then again, I grew up reading Sci-Fi, and the principle of going back in time to influence your earlier self so that reality stays the same for your later self is a well trod theme (Robert Heinlein - By His Bootstraps etc.). There ia a very clever short story by Stanislaw Lem about a group set up to police misuse of Time Travel, which fails miserably because members of the team go back and change time themselves. They lose people such as Harris Tottle and Pete Lado back to ancient Greece etc. and can't do anything about the mess they make.
Perhaps the song, Sam Hall, was a warning to he villain to change his ways or else he would suffer a fate (not worse than death, but exactly the same as...). If we go to the short stories of John Wyndham it follows that in one reality, Sam listened to the warning, and reformed, but sent himself a message back to an earlier point in time, which is still within OUR history, as a song, but of course, in OUR history, Sam didn't reform, and came a cropper, but the song remains as a failed warning!
Quack.
Geoff the Duck.