The greatest hesitation I have about the market economy is the wedge between demand and the willingness to pay that is the ability to pay. This is, after all, why full employment is so important. This is why opportunity and equality are so important. Even if we were to put aside interpersonal utility comparisons, this wedge seems to present insurmountable problems when dealing with any kind of welfare claims about the market economy. At best we can say that given these constraints individuals do their best. We can't say anything about the quality of the system as a whole that isn't contingent on implausible assumption about the quality of the distribution of the ability to pay.
The trouble is the ability to pay is tied up with productivity, and this doesn't seem to be a justifiable basis for distributing well-being. At the same time allocating productivity efficiently is the only chance of getting a surplus in the first place to distribute.
If we have robots, robot socialism is probably an answer. Until then I just don't know. Advocacy of market economies in a lot of ways is fundamentally practical. There's no particular reason to like their results except that their results just seem so good in practice. Since that's largely what we have to go on it's not a trivial point.