And as far as I've seen, the Sith rarely take the untouched. They're always corrupting other force practitioners. So they have a headstart

And as someone else mentioned, they have a lot more "ammo", so to speak. If your power comes from raw emotion, it's a bit like your ammunition being Air. It's relatively easy to come by, easy to generate, and powerful by nature. If your power comes from inner peace and balance, the tie to your power is more tenuous by nature and easily thrown. Of course, that being said, the Force doesn't seem to actually care how it's being accessed, so I doubt that it will just stop working for Jedi if they get angry. they'll just lose their skill with it, as they're having to use it differently.