It works perfectly if you use GPL'd software for a web service

I think RMS sees that as a loophole in the GPL rather than a desirable feature. Hence the existence of the AGPL.

http://www.gnu.org/licenses/index_html

We recommend that people consider using the GNU AGPL for any software which will commonly be run over a network

Or charge up front for the labor (which is inherently scarce) rather than writing on spec and charging for copies (which never needed to be scarce).

If the software is to have many users there tends to be a collective action problem in paying for it.