I don't use computers because I want to use open source software. I use computers to get something done. For example posting on a forum. Or crunching numbers. Or squishing bytes. Or storing cute baby pictures. Or serving Argentine tangos played on accordions to all music devices in the house. Or building most amazing computing devices, which are so good that my employer is willing to give me a rather large paycheck. If open source is the appropriate technology for that (meaning cost-efficient, reliable, easy to use and manage, and many other requirements that very with the task at hand), I'm happy to use open source software. It is remarkably often the appropriate technology, but not always.
If I wanted to use computers for religious activism, then maybe I would join the open source religion. But I'm not interested in religious activism.
If I wanted to use computers for religious activism, then maybe I would join the open source religion. But I'm not interested in religious activism.