I understand that delivering voluminous amounts of potable water to the masses is not an easy task and steps should be taken to make sure it isn't injurious to health, i.e. that the water doesn't have negative biological effects to the extent feasible. This is the justification for chlorine and filtering etc.

Fluoride doesn't serve this purpose. It's not there to keep the water from having negative effects, it's there to cause a biological effect in the recipient. Further unlike the example re salt and milk, where equally priced alternatives are available, the public generally can't avoid the use of fluoridated water without incurring significant expense. That's why I contend it is a medical treatment and a forced one at that.