It's not that simple. The earliest documented use of "hacker" actually did mean breaking into a (pre-computer) system. Sorry I don't have the citation handy and noprocrast (blessed be its name) is about to kick in on me. But it's been discussed here before.

So both uses of "hacker" can claim legitimacy. Perhaps that's as it should be. Maybe we shouldn't try to completely segregate the unauthorized from the creative. I'm tempted to say language knows best.

wasn't it stated multiple times that the people who break into computer systems are not to be called [...]

Stated by whom? This is the problem with the term "cracker". It's an artificial concoction (like "womyn") designed to make a point. That's why nobody uses it.