Well, clipping their wing feathers doesn't hurt them, so I don't have an opinion. If they need it, clip. If they don't, then leave them as nature created them. Some chickens simply MUST stay inside a fence or risk life and limb with neighboring animals, and clipping may be the best way to ensure that. Others don't have those issues.
Then if you do decide to clip, there is the decision about clipping one wing or two. Clipping one wing allows them to get off the ground using the lift from the other wing, but the chicken can not fly straight, usually crashes after flying a partial circle, and often decides not to try again. But they don't *always* have enough trouble to keep them from trying again, and some succeed in getting away and into trouble. On the other hand, clipping two wings keeps the bird from getting lift at all, and it stays within inches of the ground. But this way the chicken has no escape if a predator gets into the safe yard, it can't get higher than it can jump. There are pros and cons to all aspects of the "to clip or not to clip" issue.