The simple act of refusing to use proprietary software does not give users freedom in software, it just prevents them from being subjugated by that one particular piece of proprietary software. Copyleft is also not necessary to have freedom, but it is pragmatic in that it leverages copyright in an attempt to further the political goal of freedom. It would be nice if this didn't have to be done, but we cannot ignore the issue of copyright, it will not go away quietly.