Human society existed without economic incentives from the middle stone age in Africa to the dominance of the capitalist mode of production, over 250,000 years -- yes, really, without economic incentives. These "incentives" are generally understood as monetary or at least material incentives for individual work. From the middle stone age to the period, there were none of the vaunted incentives. The most dramatic improvements in quality of life also correspond to this period -- from the Mesolithic to the great temple and palace administrations of the late Chalcolithic.
According to the liberals, this is impossible as without incentives people would have just sat around stroking their dicks or something. It's simply not true that humans will do nothing unless forced by starvation. Most major scientific, medical and technology advances predate the capitalist mode of production and many of those were done by people who already had extreme amounts of wealth, or if not weren't seeking it anyway. That's an inconvenient fact to the priests of the bourgeois science, but it is a fact nonetheless.
To be clear, in socialism too, men will not be gods and will have to work in order to eat. But there will be no incentives in the sense of a monetary or material award for working more. In socialism, moreover, any increase in the productivity of labor will go toward reducing the aggregate labor time necessary for society to reproduce itself with a fixed standard of living, not toward expanding the standard of living. And we would consciously slow down improvements in the standard of living because we've seen what unbounded increases in the living standard do; instead of using the increased productivity of labor to work less and live more, we work more and more and die of stress in our fifties, but god, at least we had a phone whose battery was 1% more efficient on the way to the grave.
The real question is why do you need to incentivize labor if it isn't alienated? Incentives are required in capitalism because no one wants to be a wage-laborer, not because no one wants to labor. Marx's understanding of labor in the communal society of the future has nothing to do with capitalist work. With surplus-value producing activities eliminated, and thus probably most jobs in the capitalist mode of production, not much will be left outside of things that are necessary administrative functions or creative artistic endeavors -- and the people doing those things today would hardly stop tomorrow if socialism was instigated worldwide. To be honest, if you believe in some kind of eternal, immutable desire for luxury goods and six figure paychecks in humanity, then we're dealing with a higher concept problem.
