The point is that your system may be actively attacking another system, and it's their responsibility to immediately stop the attack first and then contact you

The point is that your system may be actively attacking another system, and it's their responsibility to immediately stop the attack first and then contact you after. If they don't do this, then they run the risk of having their netblock(s) blackholed by upstream providers or other networks, which is bad for all of their customers. They aren't responsible for making sure your system is secure, you are. You're a sysadmin now; it's not just a toy, there's responsibility too.