I am not making a moral argument. When you build more housing you use the underlying resource, which is "space". That resource becomes more scares, so everything else being equal the next unit of housing is more expensive. That is why individual area in most cities never becomes more affordable by themselves. The way to get affordable housing isn't to supply more housing as such, but to supply it from a cheaper more available resources.

Unless the underlying resource you're referring to is airspace we can definitely increase the supply of housing (and in some cases quite dramatically) without using more of the underlying resource by allowing the construction of taller buildings.

The underlying resource is space. If you are in an open field that you own with no neighbors and no zoning then the first unit of space is you pitching a tent. The second unit is another tent slightly to the left. If you are in a city were land is expensive, a prior building might have to be razed, a new advanced one planned for years and you might block someone else's view, the unit of space is very expensive. So now you have razed the building, built a new larger one and added to the supply of housing, what happens to the next unit? Everything else being equal it gets even harder to produce.

You can shift supply by e.g. changing zoning. Now you have more resources. But it doesn't change the equation, so eventually you might end up in an even worse situation were it is even harder do the same thing again. The even bigger problem however is that you don't necessarily get choose what should happen. Or maybe something is already shifting demand, like demographics.

Housing demand, despite what NIMBYs might think in the Bay Area, is not infinite at any price point. Eventually all the people that want to live in an area do live in that area and equilibrium is reached. For much of human history, that is how the entire world operated - there were no zoning codes constraining the ability of developers to build buildings for those with the money to afford them, and the king would almost never find reason to deny permits - more people in more central location meant more trade skill labor which was much more easily taxed than subsistence farmers.

You build for density until you hit the actual physical limits on density, and then you have a claim to the infeasibility of housing everyone where they want to be. We are so radically far away from such a threshold it is laughable, in much the same way some purport our understanding of the universe is nearly complete, or that we have near total mastery of our planet - neither are remotely close to happening and are just hubris on the part of those who can't comprehend how much more there is left to do.

We could have cities hundreds of stories high, entire populations housed in glass pyramids taller than Everest, population densities in excess of a hundred thousand per mile. And that doesn't need to imply poverty, squalor, or suffering - we are fully capable of building dense well. It is an independent knob of consideration that only shows correlation today because of cultural motivations and social pressure to make dense housing suck to punish the poor because only the poor live in dense housing because dense housing sucks.