IMO, a mouse can do little damage to a healthy monitor, provided that it is of proper size in relation to the size of the lizard. Like, how much damage is a fuzzy going to do to an ackie; how bad is an adult mouse going to tear into a decent sized Ionides?
Ive never had any incidents of a mouse doing harm to any of my animals. Rats, on the other hand, I give a good bonk on the head to before feeding. I dont just mean a stunning hit, but a deathblow. Ive heard of rats doing major damage. Ive seen adult mice bite the nose of my Indicaus and BT, but they rarely seem to even flinch from the mouse bite, and Ive never seen blood drawn, or even any scales lost. Mouse bite are annoying, if anything. If you think about it, out of all the mouse bite that youve gotten, how many even break your skin? I get bit by the little buggers often, and I gotta say, man its annoying as hell!! 
As far as ethics...well dont look at me on that one. I sleep well everynight.