In this case, your door being unlocked cannot cause me harm. However, an "unlocked proxy" can. Legit probes are an attempt to mitigate network abuse, not increase it. If there was a sanctioned body who was trusted to scan for such things, maybe this wouldn't be an issue. But there's not, so it's a vigilante effort.
Not completely "Vigilante", many of the Network providers reserve the right to "manage" (including probe) any network block that they -=announce=-... if not, they simply won't announce it. (While I have experienced many a probe, I have neither heard of anyone actually being declined from announcement, nor have I been part of such an experience, FWIW, but the right is "reserved".) That activity is considered by many, proper administrative "due diligence", or "managed network service". Now, if Genuity were to start probing UUnet blocks, then that becomes a little more "Vigilante"... although, in most cases, not illegal. (AFAICT) [Any comments construed as legal advice, are purely do to an errant perception on the part of the reader... illigitimi non carborundum]