It's exactly the same as Linux and open source software. I have never read the kernel source code, but I trust it way more than windows because I know others have read it and not reported any secret backdoors or exploits.
Considering the behavior of the current community I totally understand your skepticism toward the technology itself. It hasn't really proven itself useful or safe for anything but a few use cases, and the only thing it really has going for it is the theory and the core development. Fixes and new features are slowly being added to the tech to make trustless services possible.
The criticism that web3 - even if it did work properly - turns literally everything into a token-based speculative market is accurate. I think it's an emergent property of the technology that isn't good for anyone, and it's bad enough that it might be worth ditching completely.