It's hard to answer this without potentially starting a flame war. I can see that some comments start to explode already. Still, let me try to explain my mistrust constructively.
Let me just start by saying that trust is a very personal feeling. We give trust to others based on criteria that are different. I completely understand that my points listed below are not relevant trust indicators for others.
That being said, I have 2 main mistrust issues with FSF:
1) Leadership
I had various occasions to interact with RSM over the years, in various contexts. I do not have a fond memory of those interactions.
- I remember someone which is very difficult to have a real conversation with. Very childish and binary in his view of the world. Prompt to not listen to arguments, talking louder than others, turning arguments into jokes, etc.
- I worked and know plenty of people who worked with him in various academic labs where he's been invited to give talks or work on subjects. The same complaints emerged all the time: he would grossly hit on female PhD students (just enough to make them uncomfortable), always tried to be hosted by someone and would not even shower there, very rarely participate in the big picture of why he was invited (e.g. He would lock himself in a room for 2 days straight to fix some esoteric emacs bug on an archaic platform, instead of just organizing seminars on free software and participate in discussions), he would act in very narcissistic ways (e.g. After proposing to go to a restaurant, he would then propose - and insist grossly - to pay the bill with his autograph on a printed copy of emacs source code). He would constantly rant on closed source computers and cell phones, but will gladly borrow anyone's phone to make international calls. I stop here because I just have too much random echos of his not-so-pleasant behavior.
Overall most of my personal interactions with RSM, as well as friend's recollections picture him as gross, childish, and narcissistic.
Now RSM himself is not the FSF as a whole, but I have a hard time trusting an organization that is so centered around a single individual which embodies traits that I do not appreciate.
2) The organization members
I did not have direct relation with other FSF members, but I have been contributor to projects where the FSF intervened (or tried to) in the governance.
Most of the time, the FSF members were never contributors to the projects. Yet they were the one trying to dictate the tone and direction, and act like they owned the projects based on their moral high ground.
This has led me to associate FSF members as some kind of a self proclaimed elite class of zealots, exempt of technical knowledge and actual contributions, but still willing to be heard.
This goes directly against my view of governance of open source projects, in which I believe the actual contributors should be ones to set the tone and direction of the project, because they are the one building it.
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Again, all this is mainly personal feelings, so I don't want to look like I'm trying to influence others into distrusting FSF.
I understand that my interactions with RSM were in a certain context and that he maybe could be a very pleasant person in a different situation. And I also understand that my interactions with other FSF members were limited to the projects I contributed to, and there may be thousands of others where they were helping and constructive.
I'm a strong believer in "free software" as RMS defined it, and I give the man a lot of credit for getting the movement started. However, my few interactions with him were not pleasant, although I did have an interesting conversation with him once about promoting the environmental benefits of hardware running free software.
My main problem with the FSF has been more in terms of poor strategy in terms of how it engages with the software and hardware industry, rather than the philosophical vision.
A lot of FSF members I know are active contributors and are fairly reasonable, that said it definetly seems like the milage can vary wildly across the community. I have seen the type of behaviour you describe online but not much in person.
As for RMS, every interaction I have had with him.has been rough at best. I mean he is definetly right about the issues of software but him as a person can be very difficult at the best of times.
1. RSM is not part of modern FSF
2. Governance of free software projects has nothing to do with the competence of the FSF to define criteria for hardware that respects your freedom