Since smoking increases tnf-alpha, wouldn't it make sense to quit smoking if you have an autoimmune disease/disorder?

Smoking decreases : There are studies that also suggest smoking decreases tumor necrosis factor. Clinically we know that people with fheumatoid arthritis have worse disease. People with certain genetic backgrounds also have a great risk of developing rheumatoid arthritis if they smoke. There's no doubt that smoking is a killer and should be stopped for a variety of health reasons.

Always: It is always advisable to quit smoking. There are so many damages to health from tobacco in any form.