Perhaps it's just me talking, but I like my work. I like my co-workers. I have no kids nor debt, and I would be pretty sad working at a place that says that they want to fire quickly.
The hiring process sucks, and employees are human beings. Perhaps you mean to say that you should be fully transparent when someone underperforms? If that's the case, I would agree with you. No need to beat around the bushes, just be honest.
Firing quickly doesn't mean fire someone for their first offense, it means as soon as you realize the person will never be a good employee, don't waste time trying to fix the unfixable.
Firing quickly doesn't mean not to offer regular feedback, or not letting people improve, or not setting expectations well, or not being transparent. It means that it's better to rip the bandaid off instead of picking at it weeks or month ignoring the employee with the hope that things will turn around.
I guess I jumped to conclusions too quickly, but I can see how firing fast could maybe work paired with regular feedback to avoid surprises. I don't think it could work for everyone (particularly parents with young children), but under certain circumstances what you say probably makes sense.
If founders are quickly firing employees who are popular then the founders are doing something wrong, and hopefully have inculcated the kind of culture that allows them to hear negative feedback on the firing. If founders continue to fire rashly then it's a bad sign for the company in general.