Earlier quoted context omitted.
Pretty much the same as against fluorine in water in the States: it’s unnatural/a globalist conspiracy/killing our traditional way of life/a plot to subdue the people for . There is no scientifically sound reason against it.
Well, fluoridated water tastes really… well, special , and it almost feels like an indirect subsidy for the water filter industry. Iodine in salt is (to my taste) pretty neutral in comparison. [EDIT: as pointed out in a child comment, the taste actually comes from chlorine, not fluoride.]
Either way I actually do assume water filter companies lobby to keep public water as subpar an option as possible, there's certainly no incentive not to.