They banned it for use in small children as, since they would get many shots in a very short period of time, the cumulative doses would exceed federal guidelines. Also, autism was on the rise since 1975, not the 1930s, making a large spike there, and since vaccines containing mercury were around for a long time beforehand, they couldn't be linked. Besides, about 26% of the rise is simply due to the fact of many mental illnesses being reclassified from mental retardation to autism. Not only that, but awareness for autism has grown, meaning more children are able to be diagnosed for it and get treatment (which can account for 16% of the raise). The last bit to consider is that another 11 % of the rise is caused by parents choosing to have kids later, and older parents are at a higher risk for children with mental disabilities. This basically accounts for about 53% of the 600% boost in autism between 1975 and the present day.
(sourse: http://blog.autismspeaks.org/2010/10/22/got-questions-answers-to-your-questions-from-the-autism-speaks%E2%80%99-science-staff-2/)
Besides, as I stated earlier, most vaccines are available without mercury, which you can read more about here: http://www.cidrap.umn.edu/news-perspective/2004/05/cdc-neutral-thimerosal-flu-vaccine-toddlers