OK, I'll buck the trend and vote justice. In strict terms of punishment, I don't see the problem with this at all. In terms of practicality, it doesn't seem like the best preventive measure.
I don't know the details of this particular case, but in this part of the world, acid attacks on the faces of women are not uncommon. There is a culture of male sexual ownership of women over there and acid attacks are often a response to women attempting to assert their sexuality for their themselves (in ways that would go unnoticed in the West). This man being punished in this way probably won't change his sense of entitlement to female sexuality, if that was a motivation for the assault. If made permanently disfigured, who do you think he'll blame? The woman whose sexuality he feels entitled too and maybe all women in general. If allowed to go free and carry this mark on him, what are the chances he might seek revenge of this woman or all women?