I completely and totally disagree with you. As long as you've earned your money by honest means, I say to stick all of it under your mattress or burn it for warmth if you want. Is it wrong to give to the poor and the downtrodden? Certainly not. I would never knock anyone for doing so. It's certainly an admirable thing to do. No question there. I don't think there's a moral obligation there at all though.
Heck, I have more money than I absolutely need and chances are that if you're running around with a $100-200 smart phone you do do. Does that mean we should move into a studio apartment, sell our stuff, eat the store brand foods and give all of our surplus to the poor or it's immoral? Not at all. Neither one of us would advocate that I'm sure. So when does a person have "more money than they can spend"? Where's that cut off? I may already be there to be honest and I don't even make $40k a year. I prefer to live very simply though and I have no debt.
I'm not saying it's a moral obligation, I'm saying that it is moral, there's a difference.
You have more money than you need at less than $40k/yr? I don't think that you've thought that through. If you are stricken with cancer will you have enough money to deal with not being able to work, paying COBRA rates for health insurance (assuming you have HI) and the co-pays for treatment and meds? If you're involved in a serious accident, or a natural disaster destroys all of your possessions or you are wrongfully arrested and accused of a felony criminal act, etc, etc.
Unless you can easily handle any financial impact that life could possibly throw your way, you do not have more money than you need.