They all use proprietary conference hardware in the venue, right? Open source projector? Microphones? Audio systems?
Even in a security context where on one hand it's true that the tiniest pinhole is all it takes, it's also true that there is no such thing a no pinholes, and yes, 80% coverage, even 10% coverage, is better than 0% coverage.
It's a goal and an ideal not an absolute.
When you organize a conference on a location, you are using what they have on site or at best your laptop is hooked in. You have way too much to worry about to bring all your own hardware and to build out the entire media infrastructure conference in a hotel or convention space or wherever you are holding the event. That’s assuming you’re even allowed to access the areas in systems that would allow you to implement your own!
That is an unbelievably laborious task that is unreasonable to put on basically any group. At best weeks of work/installs on top of all the other massive logistic issues you’re handling. If they have a Windows terminal for you to show your presentation, you’re not going to rebuild everything from the ground up just so you can show some static images on open source software/machines. It’s just not reasonable.
That tells me more about you than it does about them. You must walk through your life extremely carefully not to do things that are inconsistent with each other.
If you rent a venue a lot of the tech needed for a conference is already going to be there — and for such a conference they will not have a ton of choices. Secondly open hardware is not very established in the conference hardware space. The reason for that are multiple, but one has to do with the fact that most of the gear requires extremely specialized build chains or equipment and you'd have to compete with decades of R&D and optimized manufacturing processes.
Your open source SM58 is going to be more expensive and less reliable unless you invest decades into it. To get out an okay microphone. Can you tell me why anybody should in your opinion be doing that in their spare time?
So maybe there is someone out there who enjoys going through a ton of prototypes to get something reliable out.
But the issue I think this is going to have is how reproducable that is going to be for your followers. I think in open source there is a spectrum: one the one side you have things like most software or simple standard-parts open hardware projects. On the other side you have things like an open source marble statue, where you still need to bring all the knowledge of how to make the marble statue — draw a circle, draw the rest of the owl and all that.
A microphone with complex coil winding and gluing a micron-thin membrane to a coil is going to be somewhere inbetween.
What exists btw. are condensor mics, but there you need to buy the membrane-assembly yourself.
How much of the actual video recording equipment was coming with free firmware — probably none — does not change the fact that these are people improving the situation rather than just accepting that the hardware you buy is at the mercy of the original vendor.