Slingshot for rabbits, birds, or to irritate any animal from moving closer to you, I would say yes. If you are shooting at anything, multiple projectiles are better than one. If you practice enough, a single heavy projectile is better. If the animal you are trying to disuade away from you is too close, a heavy stick or a stone club is better, with the first and foremost thought always being, "Don't aggravate or challenge an animal of any size that you are not sure you can overcome" (In Wisconsin, misquitoes and bees are a bigger problem than bears, so no weapon really works other than avoidance or repellants.).

I have seen slingshots with sights but since the primary rule of slingshot use is to not, repeat not line up the propelling band with your eyes, I do not really believe in the value of the sights on slingshots although I do have sights on my Shakespear recurve bow. Practice with a regular slingshot at the close ranges you can approach an animal and I believe you will be successful.

Slingshots are silent and cheap, and I would recommend buying a folding wrist brace style one and practicing an a self-made range. All you need is a heavy piece of cloth to act as a backstop and some cardboard with a target painted on it. Hang the target from some string in front of the backstop and fire away. The pellets will drop after hitting the backstop and can be used endlessly. If you get so good and consistent that you are hitting the same place on the backstop and wear a hole in it, just sew in a new piece and you are ready to go again.

As in everything else, if you practice and understand your limitations and those of the equipment you use, you will better know what works for you as opposed to what works for others.

Bountyhunter