It's unsustainable for handling small payments. Things like fraud detection, customer support, legal and financial services, and credit card chargebacks add up to more than 5%, if it's truly crowdfunding (lots of small contributions). There's a lot of failed startups in the crowdfunding space.
5% is their cut after payment processing, which is another 3% or 5% extra (depending on the size of payment, with smaller payments being more expensive to process).
For a $1 payment, they actually take 20% (10c + 5% + 5%).
I'm aware of that, which is why I didn't mention it in my list. It's about what Stripe charges. The micropayment rate of 5% is effectively lower because its per-transaction fee is $0.10 rather than $0.30. A $3.00 donation would have a $0.25 fee and a $3.01 donation would have a $0.39 fee.
Isn't it only unsustainable for VCs who want 10e50% growth ever three days?