Imagine you're on a lonely island. Would you rather eat all you can or conserve food to the extent possible?

Earth is humanity's lonely island. (I realize it's more complicated than that because billions of men on Earth do not make decisions in the same way that a lonely man on an island does. All I'm saying is that it is still more desirable to invest than save when we can, at least past some point. The extent to which society depends on consumption, perhaps excessive consumption, today, and "how to get from here to there" I don't know. I am however certain that flogging savers badly enough with high taxes will result in people burning their savings in what "from humanity's point of view" are very wasteful ways; also in people saving less in the first place by working less in the first place, also not that great - "imagine you have a business, would you rather have a worker who wants to make as much as he can and save it, or work as little as needed to survive because he can't save?")

We are clearly discussing two different things.

You are saying overconsumption by the super rich is ultimately environmentally damaging. (which i don't disagree with)

I am saying underconsumption by the middle/lowerclass is immediately economically damaging.

Prioritizing investment over consumption leads to inequality and poor economic outcomes.

I dont distinguish between billionaires and middle class folks in this respect. Overconsumption by the middle class us likely much more environmentally damaging. Does it drive the economy? Perhaps; if so, it's a problem. And certainly the Russian middle class consumes more of what it makes than European or American because lacking reliable property rights they do not trust investments to pay off.

Seems to me like an argument for sustainable manufacturing, rather than anti-consumption

Curbing consumption is immediately damaging to the economy. The better solution would be to heavily tax unsustainable business practices, rather than try to curb consumption. If you go after consumption you give more power to the super rich, while simultaneously doing nothing to discourage environmentally unsound business practices.

Why is it better to continue producing products in an environmentally unfriendly way with lower consumption of goods, rather than lowering the production of environmentally damaging products, while raising consumption rates of sustainable products?

Go after the supply not the demand.