Well, let me clearify my point of view here.
#Open-source is first of all important to see if there are no malicious codes in there. Indeed, not everyone is going to read the code (altough there should be special programs DESIGNED for inspecting and sniffing trough code) but it is also about being able to proof IF a corporation is doing shady stuff. We cannot easily prepare on how to get privacy on microsoft windows because we don't know what is in it. If we have strong suspicions that microsoft is installing crap in windows, like an AI (cortana) that listens to you, we cannot prove that Microsoft is actually doing that, they can just deny it or ignore it. With FOSS #Linux, we can actually prove to everyone if something is happening, giving the users a stronger position.
Secondly, being able to set up a program or utility without having to go trough the repeating process of asking for a license, or asking for knowledge, is more efficient. We don't have to pay a corporation to access an app or service, if we can just scroll trough the open-source code itself and duplicate that. Advancements can be made faster, like setting up independend networks.
Third, it is just a moral decision that decentralizes the abilities and knowledge of anything. It is more transparant, it is free, it is innovation focused and if it goes rogue, we can fork it.