The most effective argument for a more thorough code review is that it will reduce the potential for vulnerabilities. A code review is a process of examining and evaluating the source code of a software program to identify and correct any errors, defects, or weaknesses that may affect its functionality, quality, security, or performance. A more thorough code review will increase the chances of finding and fixing the vulnerabilities in the code, such as logic flaws, buffer overflows, input validation errors, or insecure coding practices. A more thorough code review will also improve the security posture of the software, as it will reduce the attack surface, mitigate the risks, and comply with the standards and regulations. A more thorough code review may also provide other benefits, such as increasing the flexibility, accountability, or efficiency of the software development process, but these are not the most effective or persuasive arguments for a more thorough code review, as they may not be directly related to the security objectives or requirements of the software.
References: CISSP All-in-One Exam Guide, Eighth Edition, Chapter 21: Software Development Security, page 2010.