"I renamed the printer to "Hacked" and printed a couple pages to the same effect. [...] because I was a good guy"
But you weren't a "good guy". You were an attacker.
"But still, one of the two must be dealt away with: protection by password/security/whatever, or protection of computers by law."
I'm not following you at all. Why shouldn't there be both? Just because I can lock my house up doesn't mean there shouldn't be a law against trespassing.