With the rise of the blogosphere, a greater number of people are now free to post their thoughts to the world - and because of the nature of the medium, there are a fair number of people writing about their experiences with computer software. Most software is not perfect, so some proportion of those experiences will be negative.
In the special case of free software, all end users have the freedom to study and modify the source code. (It is easy to forget, having used GNU/Linux for a few years, that the licences of most proprietary software do not even give you the right to run the software in a debugger.) This does not imply, however, that the end user is necessarily capable of debugging any problems they run into themselves (although they do have the freedom to pay someone else to do so). In general, users will rely on the original developers of the software to fix any problems - and a good way to get the developers' attention is to file a report in the project's bug tracking system when there is one. It is unlikely that the developers will learn about problems through any other means.
The constructiveness of complaints about free software can therefore be judged by whether the user has filed a helpful bug report. Doing so demonstrates a willingness to improve the software, which benefits everyone. It is the first step in moving from 'consumer' of the software to 'contributor', and potentially from there to 'creator'. But what if people aren't interested in making that journey?
A recent trend is to reply to rants with a comment to the effect of, "Could you please link to your bug report?" Writing is no less a creative act than software development - the question is asking the author to shift their creative energy away from their blog and towards the software. What should the response be if the author has no interest in helping to develop the software? It is often easier for the user simply to switch to a different program, or work around the bug. They might develop a competing program that is entirely superior to the original, or use their time some other way. Should we expect every user to give back?
If people have the freedom to help their neighbour, they must surely also have the freedom not to help. Comments like the above can certainly steer complaints into constructive feedback, or highlight trolling. I'm not sure, however, that we should expect them to build a community of unwilling participants.