In an ideal world, maybe you are right. But we don't live in an ideal world and can't pretend there is one to begin with.Don't know the details, but on the premise, it doesn't make sense to punish a lawyer for taking any case.
CPC has always been heavy-handed in dealing with dissenters. Most of these lawyers are funded by NGOs and foreign sponsors to take up cases. It isn't like they don't know what they are getting into when they take such cases. Many of them have plans to flee China and have assistance from the West to do so if things got rough.
Don't think it is any wrong for "human rights" lawyers to take up cases especially to expose corruption and wrongdoings. However, after seeing so many of these "human rights" lawyers, labor activists and women activists have become after fleeing to the West, their motives and their true intentions are questionable. Therefore, from CPC's perspective, these people are traitors and going after them are justifiable and hiding behind certain "rights" won't make much a difference.