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."
I live in reality. It's me first, then it's my family and my close friends, and then my local community and then, finally, local charities. That's how my budget works. A budget is money in and money out. And when all of that is good, then maybe I'll think about larger charities where I can't be directly involved to see where my help actually goes.
Most people do think they have less than they really do - which is to say there are families living on less income than they are thus proving it is possible with some luxury quality of life compromises. However that doesn't destroy the point that there are people at or near the bottom who shouldn't be giving.