Imho, I do believe that private businesses and companies should be allowed to discriminate however they wish- both in who they hire and who they sell to. I also believe that they'll have to suffer the consequences of such discrimination, as it is very unlikely that a highly discriminatory company will succeed. This doesn't even need to be a law. I believe this for the same reason that an individual person should be allowed to be discriminatory- they're free to represent themselves however they choose, but there are consequences for actions.
In the interest of clarity, however, I do not believe this to be the case with Public Services or Government jobs. Such things should not be able to discriminate, as they need to represent the country/state as a whole, and not just themselves.