The only time squatting alone becomes a safety issue is when you are using a seriou samount of weight and training to failure or close to failure.
The last thing you want is your legs to give out wehn you have 300+lbs on your shoulders.
There are alternatives as mentioned on this thread and working with 80% of your max and up is really only needed if working on pure strength.
There are squat racks available too.
The range of motion for squats has yet to be duplicated for EVERYONE's bodytype by any machine.
For squats and deadlifts, free weights is the way to go.
Squats ( like DL) are not just a "leg exercise" they are a whole body one that is very "anabolic" in nature.
They really get your body going.
Squats hit all your lower body, plus your abs and core and, in the case of 20 rep squats and such, they hit your anaerobic threshold.
In short, for fucntional strength you only need:
Squats
Deadlfits
Dips ( or bench press, but dips are "better")
Chins
Overhead presses.
Front squats are great and after mastering the technioque you can really work some nice poundages and over head squats give your core a serious workout.
You can also make your own "squat spotting rack" with a little imagination.
Psalms 144:1
Praise be my Lord my Rock,
He trains my hands for war, my fingers for battle !