The question is whether the cause justifies giving Amazon money--something I can't answer for everyone, but note that Amazon is not doing this out of the goodness of its heart:

"The Amazon Honor System does not charge registration fees, set-up fees, or fixed participation fees. We do, however, charge transaction fees based on the amount of money you receive. The fee schedule is very simple. For each payment you receive, we will charge $0.15 plus 15% of the total transaction amount. The person making a payment is not charged any fees at all."

Notes:
'Amazon Honor System' is a trademark.
Quoted text was found at the URL specified in the previous node although I knew about it already from an article in The Register.