I tend to see people with autoimmune diseases as having 'weak' immune systems. They seem to be more prone to infection than those who have 'normal' immune systems.

As an example, I decided to look up 'thymus and HIV' just out of curiousity one day. There seemed to be quite a few cases of people with HIV developing Myasthenia gravis and Lupus-like syndromes. In fact, some doctors were proposing that Myasthenia gravis in HIV patients be considered a disorder that sometimes comes with seroconversion. I don't know if this is happening because of molecular mimickry, in which case, it might not be indicative of a 'weak' immune system, but something a bit different, or because the immune system is being destroyed somehow and making it act wacky, or even both. There was actually a study done comparing the thymuses of deceased HIV patients to those of people with MG who had thymectomies. Pathologically, the thymuses were very similar. To me, this translated to autoimmunity being a sign that the immune system is really weak, or injured in some way.

Sorry to have diverted the subject a bit! Just wanted to share that bit of info.. I found it really interesting!