This is a self correcting problem. These diseases will strike down weak people and antivaxxers. So more diseases means less demagoguery against 300 years of scientific discoveries.
What this does in fact is create a reservoir for pathogens to mutate and proliferate, which is a danger to everyone.
Not the best link, but the abstract here sort of explains https://pmc.ncbi.nlm.nih.gov/articles/PMC2738515/