(The title is not as snarky as you'd expect; it's a distorted reference)
In case it ever comes up in debate, this is a quick, reasonable answer to the question of "Who are you to try to come up with a perspective on the public good?" This usually comes from people who haven't looked at the roots of their philosophy, and see their notion of liberty, free markets, religion, or some other thing as providing a default perspective, giving them the strategy of asserting that (because most people don't really know how to spot/tear down that argument style) and then asserting the baselessness of any opposition to it. The latter is half-right; there really are no objective answers to anything in politics, their own perspectives included. It's only the tangles of their logic that obscure that. Note that this answer assumes some kind of a democratic system (which I do not actually take for granted in all senses), but it's a reasonable start. The Answer:
Of course there is no right answer that is not bound to a perspective; we all have our notions of the public good, and political struggle is the process of reaching a consensus, for a time, on something derived from us all. That consensus, filtered for consistency (and with politically foundational people/movements given more weighting) is the basis of our legal system.
(If you really wanted to, you could frame this as "Political Science 101" and point people at sites they should read before talking to you again, but just like when certain other groups *cough* do that kind of thing, it's a disqualification argument and thus ugly, and someone might reasonably argue with its contents. If you want to rely on pre-thought arguments, do it right and memorise them or keep an argument map handy and show it to them; the idea of "you need to get schooled first to argue with me" is only potentially reasonable on objective matters like history and the sciences, not in philosophy)