okay i found a law, it states that "it is illegal to kill any snake" (without a special permit by the dnr) HOWEVER, if it is threatening livestock, or humans (vipers [well any venomous snake, but utah really only has vipers]) then you may kill it. i would leave them alone... i am against killing animals, unless its for food. (ive never killed an animal before, and i never plan on it) but if it was my life or another living creature (or human) ill choose my life, lol.
but if i was in an area that is visited by lots of little ones, campers, etc. and i ran into an aggressiverattler,i would probably kill it, for my own (and other peoples) safety.