Does open-source undermine the value of individual programmers?

As a group of programmers build open-source products they are spending time on the process but not getting paid, they then create a product, something like Joomla, which then is used by other developers. But as a whole, Joomla makes some jobs easier, but also kills jobs (or hours of work) as it takes less people and work to get a site built.

I know it makes some jobs easier, but more importantly it makes some work free.

How is programming work worth anything if it can be done for free?

What I mean to say is open-source is shooting the industry in the foot.