Why is probing for weaknesses against the law? If I walk up to a house and jiggle the door handle, and figure out whether it's unlocked or not, and do not actua

Why is probing for weaknesses against the law? If I walk up to a house and jiggle the door handle, and figure out whether it's unlocked or not, and do not actually enter, what crime did I commit? What precedent caused this to be the case? If I am a salesperson who probes for weaknesses in a customer to my own gain, am I also violating the law? What if I am an employee who figured out how to reduce my workload but didn't inform my boss, so I get to surf Hacker News more? I'm a website developer who patched 11 security holes after a security audit in my last contract gig. I think there is nothing wrong with probing. Actually breaking in and taking is another story.