There isn't really a moral grounding for any kind of diet from efficiency perspectives as we produce easily enough that we could feed the whole world if we distributed if fairly. Hell if we applied our knowledge of food production effectively across the world instead of keeping the most productive methods only to those who are on top of the wealth pyramid... Then we could feed double the planets population... and it will peak way lower than that in this next century according to forecasts.

Use of fresh water is easily boosted with desalination, a technology we have had for a very long time. Again the problem here is the people who would benefit from it don't have enough money for us to bother.

Really the only moral grounds is the carbon budget if making that much food. And again it would be entirely possible to perform all food production using non fossil fuel electricity and vehicles if we set our minds to it.

If anything, changing diet on "moral grounds" regarding efficiency is just providing a sticking plaster partial reduction on any applicable efficiency harms.

The pressure to change needs to be firmly based purely on not burning carbon to do work, everything else is just "buying time" (which it typically doesn't because efficiency savings are tiny compared to the scale of the carbon problem) or actually just giving excuses/distractions to big businesses and governments to avoid making the needed changes.

There is zero reason we should any of us need to eat insects, we have a world and technology enough to provide a balanced diet for more than double the number of humans there currently are.