Of course they're different, but the spirit is the same. Both know the risks before they start, and take the job anyway because the compensation is sufficient.
If an employer does not take sufficient (by his prospective employees' definition) safety steps, there are ways to remedy it besides legislation. The employer can pay more, to get people working in the hazardous environment. These people, with their extra money, could buy safety devices themselves. Or they could pocket it. Or they could bargain with the employer for a pay cut in exchange for the employer's investment in safety equipment. Or they could all chip in and buy the safety equipment as a staff.
With legislation, you're forcing the employer to put in the safety equipment, and through scarce resources, pay less. This is removing all previously mentioned options from both the employer and the employees.
If I don't feel that smoking is a hazard to my health, while most people do, then I have a leg up on them in a competitive job market. They can refuse the job until they feel it is reasonably safe, while in the meantime I can demand increased compensation. Legislation removes my competitive advantage, and thereby my chance at setting myself apart from and above the rest of the workforce.