The issue being, we're dealing with highly technical products (Linux, Bitcoins, Video recording technology). Rather than in the product itself, some blame lies in the developers.
Why would the developers need to be the people that promote it? In an open source community, everyone does what they find fun / are good in. If you're not a PR person you don't have any "blame" for not being good at that.In the case of Linux, it's mainly the ecosystem of companies around it (Redhat, Ubuntu, etc) that have people that promote its use to "normals", not the developers themselves.
In the case of bitcoin there is currently mainly a lot of mouth-to-mouth and media attention spreading it. But if you want to volunteer doing PR work that'd be great ofcourse
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Reminds me of the quote: "Two hands at work will accomplish more than a thousand clasped in prayer."
+1 I'm a huge fan of people that do something instead of telling others what to do or what is best to do.