I understand what you're saying here, but I wasn't saying you should replace squats with the leg press. I was saying it is an exercise that is also very effective in building up your legs, and releasing growth hormones which in turn aid in the build up of other muscles (the weight doesn't have to be specifically loading on your spine to release growth hormones, any form of weight bearing exercise will have these effects as you are forcing your body to adapt, and therefore grow). So it has those effects, as well as a good isolation of the legs (quads, hamstrings, glutes) without the stress on your back, as some people may have back problems which prevent them from squatting heavy enough to build their legs. I'm not saying to replace squats with a leg press exercise, but rather to do both as they assist each other. This also makes it a good exercise for beginners. The compression on your spine also isn't the way to go about building your back strength, nor does it build your hamstrings as effectively as say, a deadlift (if we're talking about compound movements here, not isolation). Squats target your core strength much more than hamstrings, your legs aren't your center of balance. So yes, replacing squats with a leg press machine or any leg machine is absolutely stupid, but what is more stupid is to think you don't have to do leg press exercises as well.