You would end up blocking every network then. Almost no one wants malware on their machine or network. Unfortunately, people get hacked and network operators cannot always determine which machines are hacked (hackers are not known for letting people know that they have taken over a machine).
Security is hard and there are no easy solutions. People often do not know they have been hacked or even know if a computer on their network has been hacked. Also, it is often not easy to determine if traffic is legitimate, illegal, malicious, or abusive.
Security is hard and there are no easy solutions. People often do not know they have been hacked or even know if a computer on their network has been hacked. Also, it is often not easy to determine if traffic is legitimate, illegal, malicious, or abusive.