Proprietary formats are like trade secrets. For instance, the .doc format.
LibreOffice has to reverse engineer the format. To be such trade secrets,
programs that natively work with them necessarily deny the access to the
source, hence are non-free. And yes, there can be malware in such
In my opinion, the paragraph about the GPL is totally out of topic. The
problem software patents raise have nothing to do with licensing.
I would not talk about incompatibilities with operating systems or even with
free software. You can install VLC on pretty much any operating system. It is
free software.
I would focus on the root of the problem. Maybe this article would inspire
you.
The list of free formats is an
