Those 1.8 points are 1.8 points over placebo when it is well known that depression responds particularly well to placebo. This study also only looked at first line (least side effects, relatively low effect) antidepressants, it averaged in Serzone which is a particularly weak one that was discontinued 4 years before the study, and it calculated the difference between average drug responses and average placebo responses rather than the average of differences between drug responses and placebo responses, which reduces the perceived effect.
For much more, check out http://slatestarcodex.com/2014/07/07/ssris-much-more-than-you-wanted-to-know/
Do you think that in the past depressives didn't get any treatment that's as good as placebo because they were told that their depression doesn't matter?
It's great to make people more aware of bad mental habits and encourage better ones, as many people have done on LessWrong. The way we deal with weak thinking is, however, like how people dealt with depression before the development of effective anti-depressants:
The only "anti-stupidity drugs" we have are nootropics. But the nootropics we have weren't developed as nootropics. Piracetam was, I think, developed to treat seizures. L-DOPA was developed to treat Parkinson's. No one knows who started using ginkgo biloba or what they used it for; it was used to treat asthma 5000 years ago. Adderall derives from drugs used to keep soldiers awake in World War 2.
And none of them are very good against stupidity. AFAIK, to date, not one drug has been developed by understanding and targeting the causes of different types of stupidity. We have the tools to do this--we could, for instance, sequence a lot of peoples' DNA, give them all IQ tests, and do a genome-wide association study, as a start.
We don't research these things because society doesn't want to research them. People don't conceive of stupidity as a disease that can be cured. We need, somehow, to promote thinking of stupidity as a mental illness. As something drug companies could make billions of dollars off of.