That's because the Jedi are meant to be like monks, vaguely inspired by several eastern faiths. It takes focus and meditation for them to access the force, and concentration, which is what Yoda tried to teach Luke in ESB. You can reach the force through anger and rage too, and it is a quick and easy path, but accessing the force that way will rob you of that peace, and that anger, and using the force that way, will corrupt you.
In the prequels it's expanded that there's a descent to the dark side, and that the Sith crave power for it's own sake, and in the EU it's expanded that the dark side of the force corrupts and changes the wielder, and that there are numerous philosophies regarding balance, Living Force/Unifying force, and the dark side not necessarily being evil, but those pretty much always turn out that dark side powers corrupt you, and that the dark side is seductive.
I like to think of it in the original terms. You can get it done the right way, with patience, and calm, or you can take the easy path, solve the problem with rage and anger, and in doing so, you'll learn to use that, rather than developing the patience and calm of true mastery. Yoda doesn't fear death, and happily sleeps forever. Palpatine screams like a madman as he falls into the pit..