I am very new to the 3D printing world, like 2 months. With that being said, there are always 2 sides to everything.
I agree with OP on the one side of things when it comes to open sourced things. I’ve been working in IT for 20 years and when it comes to software we never go with open source for 1 primary reason, support. When you go with open source your support is dependent on the community and not a company that you are or have paid.
On the other side of things is I guess we can some what call it “closed source” but we go with that for a number of reasons. With closed source they control what you can and cannot do.
Imagine you buy a regular printer from Brother, Cannon, Espon or HP and they limit what you can print from. Imagine them not letting you print from Microsoft word, or Notepad.exe or MS Edge or even Google Chrome.
Even worst is that the printer company could have an agreement with other companies like Libre Office or Notepad++ or Mozilla so that you could only print from those applications.
That is why most people are pissed off - it’s the uncertainty of what could happen.