Pants
Why is that necessarily a bad thing? An employment contract is a two way deal. If the worker doesn't like their terms of the deal they can vote with their feet. The worker has far more flexibility in this matter than the employer does.
Because, as history has shown, the employer has more leverage than the solitary worker. Before social-democracy came about, thanks to Marx, and the struggles which workers engaged in against the Capitalist class beginning in the 19th Century, workers had very few rights and poor and sometimes abusive working conditions.
It is only after workers collectively bargained that we have most of the rights that we enjoy today: i.e. the right not to be physically or sexually abused, laws against child labour, minimum wage, unfair dismissal laws, pensions, etc.
And you are wrong about flexibility. In most cases, a worker needs the job more than the employer needs the employee to fill it. In the former, his livelihood is at stake. In the latter, a profit margin, and in many cases, the employer has a number of candidate employees.
If you're in a position to tell a potential employer to 'stuff it', then you're probably financially independent or part of a very small minority of workers who posses a certain set of skills which are highly in demand at a certain period of time.