I'm at a friend's place and the cat keeps bringing in dead (or half-dead) animals into the house. It's my understanding that cats think we are big, helpless kittens that don't know how to hunt. Hence, they think they are doing us a favour.
It seems like a few mice actually escaped and found refuge in some walls in the house, so these "presents" are actually more than just annoying (and smelly if the dead animal ends up behind the couch).
It's not so much that they think you're incapable of hunting. It's moreso that they just like you and bring gifts. However, like others have said in here, cats absolutely should not be let outside and there is a ton of research that backs that up. The best solution is to educate your friend on how damaging their behavior is to the environment as well as how it puts their cat in danger as well. I know many people in the veterinary field and they all agree that cats should not be let outside unless they are on a harness.