Why is port scanning illegal?

Related questions

1. What is TCP connect scan?
2. How does a port scan work?
3. What is a TCP port scanning attack?
4. What is UDP port scan?
5. What is Zoomeye?
6. Is Traceroute a TCP or UDP?
7. Is a port scan illegal?
8. What is TCP FIN scan?
9. What is port scan protection?
10. Which protocol does Ping use TCP or UDP?

Tags

1. #transmission
2. #every
3. #their
4. #makes
5. #including
6. #associated
7. #legal
8. #however
9. #rules
10. #whether
11. #network
12. #example
13. #customers
14. #abide
15. #protocols
16. #hosts
17. #might
18. #completely
19. #choose
20. #scanning