Why you shouldn't be lifting with your legs (or your back)

I tend to hear a lot of; "Don't lift with you back, lift with your legs and use your knees."  I know these people are trying to spare their back by lifting with their legs but they are not using the right cues.  I found this picture about so-called proper lifting technique:

First, the picture of the "proper lifting technique" shows lumbar flexion (bending low back) which is not good for your back (I'll give it to you if you are saying that there is less than in the other example).  Secondly, the person's feet aren't flat so he isn't stable and there is significant stress on the knees with lifting like that. 

So if you should not lift with the legs, what should you lift with?  You should be lifting with your hips.  Your glutes are designed to do hip extension which is what you are trying to do when you are lifting something from the ground.  Olympic lifters learn how to lift extremely heavy weights by learning to stabilize their "core" and using their glutes to do most of the lifting. 

I'm an advocate of learning how to squat and deadlift using hips to accomplish standing.  So spare your knees and legs.  Let the hips do all the work.