Well look at the statistics:

Fluoride:

• Water fluoridation in the United States began in the 1940s
• By 1949, nearly 1 million Americans were receiving fluoridated tap water
• In 1951, the number jumped dramatically to 4.85 million people
• By 1952, the number nearly tripled again to 13.3 million Americans
• In 1954, the number exceeded 20 million people
• In 1965 an additional 13.5 million Americans gained access to fluoridated water.
• By 1969, 43.7% of Americans had access to fluoridated tap water.
• In 2000, approximately 162 million Americans (65.8% of the population served by public water systems) received optimally fluoridated water
• 2006: 69.2% of people on public water systems (61.5% of total population)
• 2012: 74.6% of people on public water systems (67.1% of total population)

Autism:

• First recognised in the 1940s
• During the 1960s and 1970s, prevalence estimates were approximately 0.5 cases per 1,000 children.
• Prevalence rates increased to about 1 case per 1,000 children in the 1980s.
• 2000: 1 in 150 children
• 2006: 1 in 110 children
• 2014: 1 in 59 children
• 2016: 1 in 54 children
• 2020: 1 in 36 children

Seems pretty clear cut to me.