TL;DR: Some devs introduce toxic code in your codebase, you shouldn't hire them. However, it seems to me proper code reviews and mentoring would have prevented

TL;DR: Some devs introduce toxic code in your codebase, you shouldn't hire them. However, it seems to me proper code reviews and mentoring would have prevented that in the first place? That's an important responsibility for the 'good' devs, and you can't simply complain after the fact if you aren't proactive in that sense.