How does GNU and free software justifies his claim that we can be in control of our software? I think RMS doesn't like Linux but being an open source software i

How does GNU and free software justifies his claim that we can be in control of our software? I think RMS doesn't like Linux but being an open source software it still can be injected with potential backdoors. What makes him think his software won't? We still review code but your average Joe cannot code and he won't code. So he's going to use a software someone packaged. How can you tell if no one will ever inject a backdoor? edit This is a major point he always makes about security. I am not buying his total obsession with GNU because that can't be prevented.