Sounds to me like what this group is doing is not extortion, it's an awareness campaign.  Crudely done, perhaps, but certainly accurate enough.  PA restaurants do have a bigger stake in this decision than other businesses  --  it's not unreasonable to remind them of that fact.

I was one of the people who changed their eating-out habits ten years ago when the city started fluoridating  --  and not, in those days, because I had a theoretical objection to the additive.  It just tasted horrible, especially in the early days when the city was trying to get the mix right.  I lived outside the city limits then, and started having my breakfasts, lunches, and drive-thru coffees outside them too.