The only "duty" your employer has is to extract as much value out of you for as cheap as possible. If you expect anything different then you are going to be taken for a ride.
An employer at a for-profit company is responsible for maximizing the company's profits, but that doesn't mean it has a duty to extract as much value out of an employee for as cheap as possible.
Such an adversarial relationship with employees causes them to leave, or at least avoid initiative or innovative solutions that are mutually beneficial to the employer and employee.
