the counter-argument is that when you fire someone, their co-workers, generally speaking, become at least a little uneasy (usually the level of unease is direct

the counter-argument is that when you fire someone, their co-workers, generally speaking, become at least a little uneasy (usually the level of unease is directly proportional to the level of agreement that the person getting fired wasn't good enough or otherwise had it coming, but there is still some unease even when it's obvious that it's the only way forward.) Now, you can try to get around this by a real trial period (either contract-to-hire, or being super clear that the trial period is actually a trial period) - if you fire an employee of a obviously lower class, employees of the higher classes won't be as disturbed as if you fired one of their peers, but then you have the contract-to-hire problem, which is that people will usually choose a job perceived to be long-term with a low risk of being fired over any sort of 'trial period' - a large portion of your top applicants will turn the job down if they have to spend time as a lower-tier of employee first.