He is not being treated that way "simply because he has a disease." He is being treated that way because he is willfully being a threat to others. There is no ethical dilemma. If he will not take proper precautions to safeguard his fellow citizens then he needs to be locked up.

Alcoholism is considered a disease too. What do we do with people who insist on driving drunk? We punish them. If his conditions seem harsh well, he has only himself to blame for that. Hopefully he'll come to the conclusion that wearing a mask while out in public isn't such a hardship after all.