That depends on the situation. There are certainly some pieces of software for which I feel that it is more important that it merely functions well at some task

That depends on the situation. There are certainly some pieces of software for which I feel that it is more important that it merely functions well at some task, and closed-source software is acceptable for that purpose. There are other situations where closed-source software makes me uncomfortable because I do not have certain guarantees about its security, reliability, or flexibility. I would say that the majority of situations are better served by open-source software, but not everybody feels that way.