I tend to believe that this whole operation is being used for multiple purposes at the same time. This way, they get the most bang for their buck.

My guess is that they added in the mercury for the "making-us-sick" part.

So many people have stopped vaccinating that it became important for them to prevent any new epidemiological data from supporting the fact that vaccines are the cause of many of the world's woes.

In short, if the autism rate drops in the population of unvaccinated children, then that would nail the already-sealed coffin shut. Now, chemtrails gift us all with vaccines so nobody begins to get healthy.