A lot of people see code review as a gatekeeping step in the software development process. They think that the reviewer is there to prevent bugs from getting into production. This is not a good way to think about it.
Code review is an opportunity for collaboration. The task of the reviewer is to work together with the author to produce great software. Identifying flaws is a part of that, as is finding ways to address them.
If the goal was to prevent shipping bugs, you could just block every change. It guarantees that no bugs are shipped – but no bugfixes or features are shipped, either.