There are probably infinite ways to define capitalism, but I would contend that the simple charging of interest on loans is capitalism -- getting money for doing nothing except tying up capital. And interest goes back further than Christianity.

http://ezinearticles.com/?The-History-Of-Interest-Throughout-Time&id=160818

We are talking about ownership of the means of production, not interest.
Profit is extracted through surplus value on labor.
But, I agree, as long as interest is involved, economies need to expand to pay that interest off.
That has been arranged in numerous ways.

"Profit is extracted through surplus value on labor."

Which means the person(s) receiving the profit have selfishly kept it for themselves and not distributed it back to the labor which produced it, or they charged too much for it in the first place. Either way, it is disgraceful behavior.

Lovely campfire post, BTW. Totally agree with it, but there are too many humans now to go backwards, and most of the damage to the planet has been done.

Actually, it is about the people doing the labor keeping the profit, not having someone take it from them. If you participated in the organization and creativity of the process, you are also part of the labor process. If you just abstractly own the means of production through a financial instrument, you are extracting wealth.