You were arguing for it. You may say you were being the devil's advocate, but you were still arguing for it. And no, it wasn't helpful, because the arguments outside the libertarian community are nothing like your arguments: they are all about effectiveness, not about principle. Getting out of the echo chamber requires interacting with actual nonlibertarians, not just libertarians guessing at the other side's arguments.
You are also badly mistaken regarding how things would work in a truly libertarian society. In a libertarian society, the extra payment required for insurance if one were unvaccinated would be based on the actual extra cost of insuring you. Since the extra risk is quite minimal, the extra cost would also be minimal. Most people would vaccinate because they'd rather vaccinate than risk sickness, but no one would be forced to, especially for the largely nonfatal illnesses that are the subject of most vaccinations these days.