You couldn't do that to a mute person, an infant or someone's pet, what makes you think it's legal. At least if it was a mute person you could try to claim you didn't know they were a mute, with a robot it's straightforward that you blinded it on purpose because you knew it couldn't respond.
The infants and pets analogy is silly. Are you suggesting that if someone leaves their unattended infant or pet on the public sidewalk, the rest of are simply to skirt and ignore it? Since we can't be sure of the robot's intentions (it's behaving erratically, has it been hacked?), and the owner is nowhere to be found, disabling it seems like the safest thing for everyone, especially if there's automotive traffic nearby and it might wander off-course and cause a crash.