I don’t know what to copy here either. I’m confused about what the official “manifesto” actually is currently. I only know about this thread and the goals mentioned on the homepage.
I also remember me creating a merge request to some document in some repository back in the day when github wasn’t part of Microsoft and I had an account there. I also remember me explicitly including “free software”, nothing else.
I think we are very much on the same page here. The commitment I’m missing from OSD is NOT about shunning proprietary software (as I totally understand the problematic limitations of only designing with free software). It is about a clear endorsement for what OSD would like to see, and a loud support for what fights the sad status quo: Free software not being a real choice in many cases 
for desigers.
An analogy highlighting my point:
Being feminist does not mean to be against men but being FOR women.
OSD guidelinbes/manifesto/goals just lack something along the lines of:
“We like free software and support design being done with free software.”
Please note how this is not saying we don’t accept people or their contributions when they are done with proprietary software. It would just show our ethics when design meets open source.