You have way too much faith into the the idea, that open source projects are free of backdoors / exploits and that the community can prevent creation of those. Aside from that, there is currently no platform, where 100% code is open source.
Of course we can't. But we are in a vastly better position to positivity affect these things if we do have the source.
It is immaterial whether or not any platform is currently 100% open source. rms_returns is right in noting the discrepancy between noble apple sticking it to the man and walled garden apple sticking it to the user.
