In Tuesday’s San Francisco Chronicle, columnist Jon Carroll went off on an ad that’s run lately in his paper and others promoting a drug to treat rheumatoid arthritis. The drug is called Humira, and Carroll is aghast at warnings in the ad, which advise that people taking this drug might be at risk for fatal infections, heart failure, and “certain types of cancers.” “I look at the risk-benefit ratio, and I worry,” Carroll concludes, and understandably so. Rheumatoid arthritis is an autoimmune disease,…