There are a number of principles of public health policy. The one I consider to be the most important is "healthcare for all." The fact that someone is not born into a well-to-do family or doesn't have the means to provide for his/her healthcare should not exclude him/her from appropriate healthcare. This principle is influenced by humanism, i.e. all human beings are born equal and hence should have the same rights and access to the same services. Often there is debate over why the tax-payers should foot the bill for others, but the counter-argument is that it is always the responsibility of society to take care of its less fortunate constituents. One can also argue that people with means will be able to get the service anyways, however the less fortunate will have to be taken care of by the society and hence should get the maximum benefit out of any public health policy. There are some countries where public healthcare is available for all the residents. Then there are countries where no public health policy exists. I would choose the responsibility of haves towards have-nots as the most important driving force for healthcare for all, as the primary principle of public health policy.
Hope this helps.