No the problem is not unsustainable consumption, the problem is unsustainable production. Production = consumption + waste, and about 40% of all food is thrown away rather than consumed. And not just that, but food waste is growing faster than food consumption. And yes, contrary to what the over-consumption crowd would have us believe, it is indeed the production of food that is having the environmental impact and not the consumption of it. Leading us to...
We already produce over 33% more food than is needed to feed everyone. But, us living in a capitalist economy and all that, it just happens to be more profitable to throw it away than to use it to feed people. Of course such a position would require structural analysis and anti-capitalism, so who would ever want to do that when, instead, you can just moralistically finger-wag random individuals enjoying a steak? And deity forbid it would actually entail finger-wagging the capitalists - you know, those people who actually profit off producing food waste while millions starve to death each year - rather than finger-wagging your own class and we can't have that, can we?
Overpopulation rhetoric is eco-fascist nonsense, overconsumption rhetoric is liberal nonsense.