You are absolutely right, someone with another job offer and money in the bank can walk anytime, but of course we know this ir rarely the case.
This is why we need some sort of regulation that covers temping and how long companies can keep one person at temp status.
Companies absolutely should have the right to hire people on a temp basis to see if they are a good fit with the company
and companies should absolutely have the right to hire temps during busy periods like Christmas when they need people short term.
but
Temping as a permanant status for an employee is just a way of skirting around benefits and fair pay.
In reality we all know that, and how you view the issue comes down to whether you are a worker who needs fair employment laws or an owner / shareholder whose sole interest is in the profits from a company.



