Doesn't matter. That's what the majority of people are using; so if you want the marketplace to actually be able to serve people, and get them to actually buy stuff, you need to support them.
What the majority of people are currently using is irrelevant. The whole topic of this thread is creating decentralized markets, and you're saying the fact that these payment processors are centralized doesn't matter. That doesn't make any sense.
It sounds like a good compromise would be to allow people to check out with a credit card/paypal and have an instant conversion to BTC behind the scenes, maybe with a 2% fee or something.
But a decentralized market does exist with cryptocurrencies.
And credit/debit cards aren’t decentralized.