That was a cruel and selfish thing to do.
Blinding that mob boss wouldn't make him any less dangerous. He'd still be able to use his financial influence to have people killed. Only now, he'd be embittered and likely even more deadly because something of value was taken from him and can never be returned. If anything, he'd be more aggressive as a result. He might not be able to wield a gun himself, but he can more than afford to have others kill on his behalf.
Not to mention that intentionally blinding another person would be an inhumane thing to do in and of itself. In what world did they ever think it would be justifiable for the hero to do such a thing?