I think it's important to have boundaries. If we keep our operating systems fully free, it will be harder for anyone to pressure us to add proprietary components to them. But if our OSes already contain non-free components, it's not that hard to add more. We not only want freedom, we also want to keep it.
It also needs to be clear for the people in our community that our main goal is freedom and getting rid of proprietary software. Convenience is less important.