My supposition is not about caring about the quality of work at all. You totally missed the point. It is about being upset about things and not dealing with it in the right manner.
If this developer is breaking the company, then it is your job (while you were there) to mentor the developer. It isn't about the code at all, it is about the culture of the company to tolerate the behavior that the developer is exhibiting.
What you describe as a problem, is such a general common problem in this industry that as a more senior person, you should have been able to help define better.
Once you have the policy in place, it is much easier to go to the CEO and say... "hey, we've put these policies in place, everyone agreed to them, i've tried to mentor the developer and nothing is working. i don't think this person is beneficial for the business."
Until you do that, it is he/she/they said and the likely non-technical ceo has no understanding of what good/bad code practices are.
I'm also a contractor, been one for ages now. I only take a 'real job' when I'm a founder. I've got perspective on both sides though.