Are Smith machines superior to free weights?

The main argument against the Smith is that it locks the body into an unnatural range of motion. If you analyze a free weight squat, you'll see that the shoulders shift their position relative to the rest of the body due to the natural change in the center of gravity. A Smith won't allow this deviation to take place.

If you try to load the Smith like a regular free weight, you'll have to bend forward on the descent. Knowing this fact, you can actually position your feet forward a bit and lean back into the Smith and minimize this impact.

Are they better or worse? They are just another tool. It depends on what your focus is. I don't like them for squats because they encourage imbalances. Many people have upper body imbalances that cause the bar to become uneven with free weight squats. Squatting and compensating is an effective way to counteract those imbalances. The Smith keeps the bar straight and doesn't allow for the deviation, so the imbalance can persist.

On the other hand, let's say someone wants to bench press but has a prior rotator cuff injury. Depending on the type and extent of the injury, the Smith is sometimes a good choice for benching. The issue with benching is that the shoulder joint stabilizes the upper arm during the movement, and sometimes the weight may suddenly shift towards your head which results in rotation and possible injury/tear to the rotator cuff. The smith will lock the bar into a plane of motion that does not allow this rotation. They're also great for calf raises, seated calf raises, etc.

I'd say asking whether a Smith or free weights are superior is like asking what is best to clear the sidewalk - a rake or a shovel. It depends on if it is Fall or Winter.