Did anyone suggest it was? That seems like a very weak straw man of the very many sensible arguments from multiple angles, for why vast wealth inequality is a bad thing for society, including the members of the society with the extreme wealth but surrounded by poverty.

I think it exactly contradicts that:

Wealth gaps are a sign of wealthy societies — the question is wealth distribution, not distance from the lowest to highest.

You can have a large wealth gap, while still having a high bottom standard of living. A great example of this is Sweden https://www.youtube.com/watch?v=2E0dWHCnic8

Supplying handouts does not affect the wealth gap - giving the needy some real capital like own housing, shops, etc would actually contribute to that goal. Handouts don't help enough because the money is spent on their necessities (which was the point), and obviously that means the money immediately flows to the rich ones that supply those items (housing, food, etc).

Reducing the wealth gap is crucial, I think you're severely misunderstanding.

Yeah, this is an unfortunate side effect of many social programs. Eg. housing assistance is just money that (1) goes directly to landlords and (2) removes market pressure and keeps prices for low quality housing higher than it should be.

Way more effective would be caps on rent, but for some reason politicians don't want to use this tool....

Caps on (housing) rent suppress development. Caps on rental profit (economic rent) suppress profiteering.

Let's imagine this in the most extreme form in a thought experiment. An identical twin is stranded in the desert. You have the means (water, transport) to save one of them. Is it better to save one (which one?) or leave both to die? (I have not settled on a firm answer so far.)

Any value system in which "save one person" is not obviously and objectively better than "save zero people", with no other tradeoffs or details present, seems objectively incorrect.

tbf real world tradeoffs are usually more like "save one person with high degree of likelihood of success" vs "attempt to save two people with significant likelihood of failure"

If there are 10^58 people in the second situation we call them longtermists.

The result from this study: Give one a glass of water, and the other may end up swimming in a natural oasis -- both live & have better lives.