I don't think money should be the drive for anything. Money is the medium that we use to fuel our ongoing contributions to society. So why close your source?

Money is almost always synonymous with power and that's not necessarily a bad thing. You want power to do what you want and need.
Without this kind of incentive you might lose interest, few will be willing to help, might no think well enough of the end user (UX).
Also it clearly doesn't work for most software, it's usually quite bad and no competition to proprietary software. ( Does anyone seriously think gimp is alternative to photoshop?). It works for software developers use, developers make what developers need.

There are problems inequality creates but making money shouldn't be a sin.

I never said money was bad, I just meant, more broadly, people don't live for money. I think it's obviously very important, but it shouldn't be the main goal of our projects.