Among Effective Altruists, we have seen that it’s a rationalization they use to justify greed. That’s the context. So parent is saying that this rationalization isn’t helping anyone.
Another way of thinking about it is, do you think the honest people living the lifestyle choice you describe, would they be out there telling people how great they are for doing it? No, they’d be focused on their work, to earn, and to give.
But here they need a “movement” to validate themselves, because at some level they know they are just selfish people.
(See related rationalization where highly successful founders and investors that decline to give to charity because they are “investing in their next venture that’s going to make far more money and then they’ll give more to charity” when they have more money than anyone needs and the world needs help NOW)