There's a lot to be said about the strengths and weaknesses of open source (and source available) software but to me it comes down to one simple thing:
*If the company doesn't trust me to be able to see the code then I don't trust them or their code.*
Notice how I'm talking about trusting the software and not about using it. We don't live in an ideal world and sometimes I have to use Google or Microsoft stuff, which I try to keep to a minimum. But that doesn't mean I trust them.