First,, I personally prefer the OM's by far. But I also have enough NM's to make me happy.
But I occasionally hear about how a hunter scares a deer when trying to cock the hammer of a SA. (Like mentioned above.) I have hunted AND killed deer with a SA,, and a couple of them were VERY close when I cocked my Ruger. One doe,, I could have almost smacked her with the barrel when she walked right beside me. She never reacted to the careful, slow, glove covered Ruger as I cocked it. And as my hammer was getting pulled back, my thumb went in between it & the frame until I was ready to SLOWLY raise the gun to shoot her.
Other times,, I've seen movement,, and done the same slow cocking method,, and gotten ready long before a deer got close.
I think it's all in HOW you choose to cock the gun, as well as when you do so.
And while I've never spooked a deer when using a SA & cocking it,, I know it may happen the very next time I try it.