I remember being in Sea with the Linkshell and waiting for our tanks to get charmed so we could unleash WS and nukes on them just for shits and giggles. It's was fun time to time as long as the fights weren't getting chaotic. Then we'd only aspir the tanks <.<

"Stop stealing my MP!!"

However, I never attacked charmed players outside of our Linkshell/party. And imo doing so is really a NPH move. The only place I guess it would be mildly acceptable would be Besieged; and even there I'm betting people would still be upset.