“Don’t mock the afflicted for you will/could be afflicted yourself”.

This says that you would not want to be sick so you should act towards the sick with compassion. But you can turn your sickness to your advantage.  Under some conditions you could be glad to be sick. The terminally ill enjoy life better than we do because what time they have left is so precious to them. The saying contradicts the Christian view that sickness can be a gift from God and a good thing. Christianity teaches that God works to turn all evil to good.

The saying presupposes that you should not be sick and others should not be. It suggests that sickness is necessarily bad.
 
If you are freely cruel to the sick, free of your own free will, then you deserve to be sick so the saying is morally defunct.

Also, how likely is it that you will get the sickness you mock in another person? If it is improbable then the saying becomes useless. All right and wrong depends on the calculation of probability and the saying is denying that. It would only be wrong then to mock if it were probable that you would get the sickness yourself.
 
Person A, "I should have killed that person when the king asked me to. He said if I did that he would spare the fifteen people. I refused so it is my fault".
 
Person B, "You are not responsible. Nobody made him do it. You didn't know he was going to really do it."

Reply: You believed he would do it. You knew you would probably be causing the deaths of those other people. You are as responsible as he was. If you had killed the person the others would still be alive.