Arthritis is the immune system attacking your body parts. Would it not
be smarter then to have a weak immune system?

which would you rather have: a stiff right arm or pneumonia?

Actually human immune system acts in 2 ways. Humoral & cellular response.
When an antigen(bacteria, food allergy, chemicals) enter the blood
stream, a humoral response is triggered. Which is what happens in ALL
healthy people. When the humoral response is overwhelmed, the cellular
response kicks in with a 'Shoot first, ask questions later' approach.
This is what causes the arthritis or for that matter any auto immune
disease.
A strong immune system is able to tackle any offenders with just the
humoral response. A weak immune system lacks the humoral response but
possess a high cellular response. A compromised immune systems lacks
the ability to respond at both levels(this is the level when cancer,
AIDS appear).
A strong immune system will take care of arthritis and other symptoms
ailing the patient.

Firstly, rheumatoid arthritis is your immune systems attacking
yourself (autoimmune). Osteoarthritis is just degeneration seen in
older people not an immune disease.

In rheumatoid, the problem is that your body has made antibodies
against some of your own cells. The antibodies attach to normal
healthy cells in the tissue surrounding the joint. So its a case of
mistaken identity. The body thinks 'This is an invader. Attack it.'
And so it does. So a weakened immune system does help in this case,
and doctors will give immune suppressants. The downside is that you
then become at risk of other infections because your normal immune
response has been weakened.

Hope that helps.

Ignore what thinkcap-ga said; that description of the immune system is
very wrong, indeed, and yet it does not address your question. First,
a healthy immune system consists of both a humoral (antibody)
response, and a cell-mediated response. Contrary to the aforementioned
comment, the humoral response is not capable of handling all invaders.
A humoral response consists of antibodies that attack particular
"foreign" substances; for a humoral response to be helpful, the
foreign substance must be in contact with the antibody; such as in the
blood stream, on a mucous membrane surface, etc. There are some cases
where the foreign substance (such as a virus or bacteria) are INSIDE
cells, and not in contact with circulating antibody. In those cases,
the cell-mediated response serves to kill infected cells, thus
preventing further reproduction and spread of the organism.
Cell-mediated immunity is CRITICAL in fighting off certain cancers,
tuberculosis, and most viral infections (which all require a phase
within body cells). Indeed, in these cases a strong humoral response
may be useless, and the cell-mediate response your best hope.
In rheumatoid arthritis, complexes of antigen ("foreign substance")
and antibody lodge in the joints and synovial membranes, which sets up
an inflammatory reaction. These antigen/antibody complexes can lodge
in other places such as the skin, kidneys, brain, etc. and have
pathology there. So indeed, as another commenter stated, rheumatoid
arthritis is essentially caused by mistaken identity by the immune
system; one of the cornerstones of treatment is selective suppression
of the immune system; but this comes with a cost. Regards

Just because you have a weak immune system does not mean that you
could not make an antibody that induced rheumatoid arthritis, and
conversely, having a strong immune system does not mean you will
produce an antibody inducing rheumatoid arthritis.

I suggest you ignore the armydoc who has the least idea of how to
prevent the beast from attacking your joints. I've successfully
recovered from a 2 yr bout of rheumatoid arthritis and now gaining
full health. I have dealt with people like armydoc who know all the
theory but fail to find a solution for this dreaded disease. Not only
me, many others have put their RA in remission following a particular
protocol(sorry armydoc, this protocol doesn't need white coat doctors)
and now successfully living happily PAIN-FREE.
Now coming to armydoc's textbook comments, he needs to think on a
couple of questions:
1) Why is the body's humoral response overwhelmed in the first place
that a cellular response is triggered?
2) What can be done to increase the humoral response? Antibody antigen
creation is a cellular response and not necessary at all. What's
causing the antibody-antigen creation? Answers?
There are more graceful and extremely safe methods to avoid the
antibody-antigen creation rather than taking a weekly dose of
methotrexate. And that is the answer to putting this disease in
remission.