"Port Scanning is NOT considered hacking and is perfectly legal"

Not arguing with that statement; but ISP's don't approve of it.

Our previous ISP "had" a help-desk staff who scanned our ports, on a regular basis. He got fired after being reported.

They feel it's like walking down a street, and testing all the doors and windows of the houses to see if one is open.

Why test ports (or doors), unless you are looking for an opening ?
(or testing your own weaknesses)

My 2 cents worth.