Once an account is already vouched, it will likely face far less scrutiny on future contributions — which could actually make it easier for bad actors to slip in malware or low-quality patches under the guise of trust.
It's not a perfect solution, but it is a solution that evolves towards a high-trust network because there is a traceable mechanism that excludes abusers.
My comment was just to highlight possible set of issues. Hardly any system is perfect. But it's important to understand where the flaws lie so we are more careful about how we go about using it.
The BGP for example, a system that makes entire internet work, also suffers from similar issues.