To clarify:

You can use GPL licensed software and sell it. There is nothing preventing you from commercially exploiting GPL licensed software. In fact there are plenty of companies doing so. You just have to include the source.

You might find this less attractive for your (commercial) goals and needs, but I find it quite attractive and important to have access to the source and the possibility to alter or enhance the software I use, while preventing freeloading (not quite true with GPL, see services as a loophole, AGPL is actually even better at preventing freeloading) to a certain degree.