...and attitudes like that just result in many people not using any free software at all, when they could instead be running free programs on a non-free platform.
This is, sadly, self-defeating. If Emacs were widely recognized as the best editor (or whatever of its myriad functions you use it for), "works best on GNU/Linux" could advance the cause of free software. As it stands, though, "only works well on GNU/Linux" instead just means that fewer people will be using it.