I've short started my barrel several times, back when I first started shooting it, without apparent damage. I've always used pretty light charges (50g FFg in .50) , though, as the rear dovetail is just a hair deeper than I'm happy with (though safe enough, according to an experienced smith I showed it to).
Next gun and setup I make, I'm either going to find a load/crown combination that doesn't need a short starter to shoot well, or use a knife handle to start the ball a la Audubon's description of D. Boone's loading technique. I suspect that it would be a lot harder to forget to ram the ball if it is sitting right at the muzzle....Personally, I like the idea of shooting a muzzleloader in a way conducive to doing so under stress, or when exhausted, or cold and hungry - pretty normal conditions for frontier marksmanship - but I have a family that reminds me from time to time that I am a nut.