Earlier quoted context omitted.
The problem is that their individual virtuosity (or frugality) can hold back the economy as a whole (and poor people might suffer most from that). This is Keynes' Paradox of thrift. https://en.wikipedia.org/wiki/Paradox_of_thrift
Perhaps we should rethink the under pinnings of our culture rather than continue pushing "excessive material consumption"? Seems strange to live on the notions of man who lived before today's environmental concerns became cause for alarm.
However, these individual actions might collectively have unintended consequences, and that's what the paradox of thrift is about. It's a descriptive concept (i.e. about what happens in the real world), not a normative one (i.e. what people ought to do).
But before you decide what one ought to do, it is best to take into account what actually happens in the world.
It might well be better if people spent more (and that need not be on material things, it could be education, concerts, and so forth).