In discussions or debates, a common tactic against free-marketeers is to demand some sort of guarantee that the market will solve X backed up by a detailed, step by step, explanation of how it will be done.
Only those who have not deeply understood its purpose will ever attempt to provide answers to the whats and hows of a free-market. For as the wise have said, if it could be known how the market would solve something, or even what it would deem worthy of being solved, then this would be the greatest case against it.
If we could predict the free-market, then we wouldn't need it. The whole point of a free-market system, with its prices and costs, profits and losses, is to tell us what we need to focus on and guide us in the intelligent use of resources.
There are those who think they know. They know what society should do and how. So they don't want a free-market (that could prove them wrong). Us free-marketers, on the other hand, are the ones who accept that we don't know. And, when we think we might know something, we're the ones willing to put our theories to test. If we're right, we profit. If we're wrong, we lose. Simple.
The correct response, in my view, to those demanding the impossible, is to ask them "How do you know that solving X is the best possible use of our limited resources?".
They don't. They might say how important and wonderful it would be to have X, but so what? There are quite a many wonderful and important things out there. How do you choose intelligently? By pretending to be really smart and having the best of intentions? I don't think so.
You need prices, you need profits and losses, and you need the freedom that allows information to flow efficiently.