I didn't know that nightshade vegetables were bad for people with arthritis. I have Arthritis in the knee because the cartilege has worn down. I don't know if not eating nightshade vegetables will help with knee pain, but I certainly will eliminate them to see. I read up on nightshades to find out what vegetables they include, and found that they include the following:
* potatoes (not sweet potatoes)
* sweet and hot peppers (including paprika, cayenne pepper and Tabasco sauce)
* ground cherries
* tomatillos and tamarillos
* garden huckleberry and naranjillas
* pepinos and pimentos
From what I read, sweet and hot peppers include bell peppers, too.
To answer your question, no you don't have to always live without eating nightshade vegetables. You can accept living with the pain and still eat them.