I could get into virtue ethics or religion but I know this is Hacker News, so maybe I can frame it like this:

Telling people to wait until they're financially stable before giving risks creating a dynamic where people never start. The person who says "I'll give when I can afford it" at $30k is likely to say the same thing at $100k, because the scarcity mindset scales with income.

Small-scale giving early on helps build the identity and habits of someone who contributes to their community rather than just consuming from it.

And arguably there are network effects formed from generosity of time/money that can bring long-term benefits as well. It's a spicier idea, but I could even suggest that giving helps you see money as a tool rather than as security itself.

This comment perfectly illustrates the mindset folks are talking about. "I'll give when it doesn't hurt me so much" is another form of "I'll give when I have more." It doesn't make the person "bad" or any such thing for not giving, but you won't convince folks to not give by saying "but what about you, don't you want nicer food/clothes/etc."

> give what you can when you can