The legality bootnote can also be interpreted as a possible / likely cover for such a DOS:
"against something you don't own"
The underlying principle of any fake AP is to persuade people that it is the AP that you own. Of course it's demonstrable that you saw through the subterfuge but that would require the fake owner going public about his activities. In the more likely case that he doesn't want any more trouble you can just validly argue that you were carrying out a legitimate vulnerability to DoS attack on your own system!