A bad hire can easily cause more friction than if nobody was hired at all. Net effect for the business is negative. You're also probably severely overestimating the likelihood of a bad hire going through.
But the cost and other effects of doing so vary significantly depending on where you are. Most of the US may have at-will employment, but much of the rest of the world does not.
But the US is the place where the "It's better to reject a good candidate than hire a bad candidate" mantra comes from! European companies practice it, but they do it because they're forced to, and they don't preach it like a gospel. The US does it without any need to do it, and thinks they're gaining some sort of advantage in the process.
We had a really bad hire about 2 years ago. So bad it caused us to review our entire hiring process to understand how he got in. It took almost a year before he was fired (and he was a contractor so it should have been easier). In that time, he used up untold resources while we tried to find work he could actually do, people helping him "just in case he just needed a helping hand" and so on. Finally after wasting other people's time for 9 months, a manager made the decision to get him out.
A year later I got an email from him asking for a recommendation. Nothing ventured, nothing gained I guess.
Here I see the same logic that caused the TSA. Some rare and bad event happens, and people rush to rebuild the whole system to never let that happen again. Not even considering maybe accepting that rare and bad events happen and dealing with them more efficiently would be better? Maybe rebuild actually doesn't even prevent bad events, just specific type of bad event that already happened and is unlikely to repeat anytime soon? Maybe dealing with imperfection is better than trying to be perfect every time?
I.e., I don't know your particular situation, so I wouldn't dare to assume the reaction was wrong, but too often "we much at all costs make sure it never happens again" overwhelms any attempt at reasonable approach and cost/benefit analysis completely. Maybe getting one bad apple in occasionally is a reasonable price for quickly and efficiently hiring a lot of good people?
Because it's hard to fire someone. Lets discount the emotional cost completely and simply look at this in terms of financial risk to the company.
Employee X is hired. After a month it becomes clear to the whole team that X is a bad hire. But how do you turn a subjectively obvious feeling into an objectively obvious reason to fire. Because if that person decides to sue the company after getting fired that's what you will have to demonstrate.
Just imagine how hard it is to quantify what makes someone good at our job? Code Quality? Team dynamic? These are really fuzzy metrics.
You could document how many times the engineer affected production badly and how much that cost the company. But to be realistic even great engineers do that. Heck I touched production at Google and decreased revenue by millions of dollars and it was expected that this happens. So you'd have to let him affect the company enough times to be obvious He's worse than your other engineers.
You are going to have to have documented enough clear failures to do the job to justify starting the process of firing. If you don't have a performance improvement plan then you might be able to speed up the process a little. However not having a performance improvement plan is both a bad idea and, I would imagine (IANAL etc.), could cause problems later on down the road in a potential suit.
Taken in that light 9 months doesn't seem that long at all.
Idiot: We don't want to make any bad hires! Therefore, we reject a lot of good candidates!
FSK: If you pass on many good candidates, and you have a small chance of hiring any given bad candidate, then each good candidate you reject actually INCREASES your odds of making a bad hire.
Idiot: We made a bad hire once! Never again! Now we reject lots of good candidates to avoid that repeat disaster!
FSK: But, if you want to minimize your bad hire rate, you also have to minimize the number of good candidates you reject.
Idiot: NO! NO! NO! The way you make sure you hire no bad candidates is to be so strict that you reject lots of good ones! That's what everyone told me so it must be right!
In one ear and out the other. Why do people who don't understand statistics get to be managers? If you don't understand this statistics argument I made, you're unqualified to work in any sort of technical area.
It's actually fairly reasonable. The manager doesn't want to avoid hiring bad candidates. The manager wants to avoid being blamed for hiring bad candidates. They want to be able to say "I looked really really hard for reasons why Bob was a bad hire, and didn't find any, so you can't blame me for Bob being a bad hire."
Whether or not this actually reduces the number of bad hires is beside the point. It's a classic principle-agent problem.
You're missing something vital here. They're not rejecting good candidates because they're good candidates, they're rejecting them because they're not sure enough that they're good candidates.
They fear they might be bad candidates. They'd rather reject too many than too few, so they make sure they reject everybody who they're not 100% is a good candidate. That means they may reject some good candidates that aren't easily identified as such, but it doesn't increase their chance of hiring a bad candidate; it decreases it.
Strictly speaking, I think raising the standards also could lower the probability of a bad hire (depends on the model - is bad hire completely random? does it depend on some parameter that is controlled?) together with a probability of a good hire, so I'm not sure it is a robust argument that raising standards always raises chance of a bad hire. I'd be happy to see a more rigorous proof (I know it's complete waste of time but for some people it's fun).
Basing all of your management decisions purely on statistics is a bad strategy. You're assuming that the weighting of good vs. bad candidate is the same, when they're not.
Hiring a good employee is not nearly as impactful as hiring a bad one. If you can have a strategy that filters out 100% of bad employees, but unfortunately also filters out 90% of good employees, this is preferable to filtering only 50% of good employees, but also only filtering 90% of bad employees. You may have more good employees with the latter strategy, but the bad employees can kill the team.
People have an irrational belief in their ability to tell the difference. This is how one gets such flawed thinking in the first place (regarding priors and probability distributions).
Firms are hierarchy-based entities. "Technical Merit" is about a third or fourth order away from what really drives the hiring decision. Its also very imperfect predictor of actual performance.
The issues is that companies use the term all the time. They want people to believe they were hired for their merit, but merit is almost always 'fit' and not technical in nature. The technical hoops are just a CYA for when the 'fit' doesn't work out (mis-judgement) and they need something to point to as to that is not arbitrary in nature to explain how other people were not hired instead.
A bad hire can easily cause more friction than if nobody was hired at all. Net effect for the business is negative. You're also probably severely overestimating the likelihood of a bad hire going through.