The employees can choose to work elsewhere. That is the key fact that you are missing/purposly ignoring.
There's this little issue called the law. It protects workers in the workplace against harmful agents, and unsafe practices. This is covered by OSHA. The particular section you would be interested is here:
http://cobrands.business.findlaw.com/human/nolo/faq/1710112D-A8C2-4DBC-97A3E271E3C8A169.html
To say that if someone doesn't like, they should quit and look elsewhere carries little/no weight. The law applies to everyone, whether we like it or not.