So, there’s nothing special about making more money than is necessary to “survive” and “be comfortable”, right? That is a non-argument in favour of progressive taxation, or even about taxation in general. Nothing special happens at that particular income level.

“Being essentially ‘middle class’ is more justifiable in a world of poverty than being very wealthy.”

This is very useful as a strategy to dodge criticism of a line of reasoning, and to avoid having to apply it fully on oneself: to draw the line just above one’s own level of income.

If this is a “world of poverty”, as you say, being “middle class” in the US or in Spain puts one at the top. You and I are still “rich”, by global standards. If, as you suggest, making more than enough “to survive and be comfortable” makes it moral to force redistribution of (ie, taxing) all earnings above that threshold, you and I should be donating every extra dollar we make above that threshold. But then, if we did, we would stop being “middle class” very quickly.

I see contradictions in your argument.