Companies are the de-facto vehicle to do something interesting and worthwhile together while making a living out of it as well.
Why not take that some steps further and divorce the concept from the often more mindless than not "we have to make a profit!" shareholder value yaddayadda...?
As for trusting the OS, it is true, but I would argue it is no better than running on an Android phone that you don't compile and deploy the OS for. There can be a hardware backdoor in your phone too. At some point, you will have to trust your infrastructure to a degree.
It's hard to trust anything after Snowden. I don't know why my smart phone wouldn't be spying on everything I say. If not now then next year.
Maybe for messaging, what's most important is decentralized anonymity. We can use code language to conceal secrets. For actual documents, we can use more trustworthy platforms, at the very least ones with non-secret operating systems.