Nothing wrong with using a Smith Machine for squats. Especially if the machine is angled at about 10 to 15 degrees. The movement will be the same as squatting with free weights. Plus it is safer on the machine.
smith machine squats are fine. are they as good as free weight squats? NO. will you still get 90% of the benefits from doing them in a smith machine? yes.
and they're NOT safer. in fact, because of the fixed range of motion, the lifter can use his joints as leverage against the fixed position and do MORE damage than if he had to lift the weight through his own range of motion.
the myth that machines are "safer" than free weights is just a lie told to the masses in order to sell useless fitness gadgets to fat soccer moms......and they make millions. and people still perpetuate these myths because its been drilled into their head by infomercials for decades.