Cutting people down in an attempt to push them to greatness is not something I support. Encouraging someone you see potential in while being honest is way more beneficial. It might even be what transforms someone from ordinary to great because it gives them that extra boost to believe in themselves. Fletcher (Simmons) says at one point "there are no two words in te English language more harmful than good job" and I am inclined to believe. Placating someone so you don't hurt their feelings doesn't do any good but you don't need to call them a "cocksucking piece of trash" when you are being honest.
The point I took from the film was not that we should berate and torment ourselves and others to reveal greatness but that those who want greatness will overcome every obstacle. Fletcher was an obstacle analogous to many things life throws in your way but is not a suggestion for how we should interact with others. Passion isn't something that has to be beaten into you. Either you have it or you don't. Adversity simply reveals how much heart you actually have.