That's right. After I get as big as Microsoft, I can still refuse to hire left-handed redheads. I gather you believe that statist intervention in my affairs becomes justified when my company exceeds X employees?
It was not a law that prohibited discrimination. It was a law that AUTHORIZED discrimination. It said that you CAN discriminate against gays.
I agree that such a law would be redundant: your right of free association already implies that you can hire whomever you please. I also agree that the law doesn't go nearly far enough: by singling out gays, it implies that your right of free association is curtailed in other respects. But it's the existing laws curtailing free association that make such a law seem necessary.
You only needed this statute if you did not have a Constitutional right to discriminate.
What confuses the issue is that the right of free association (what you call the "right to discriminate") has already come under attack, and been weakened in some critical ways. This leads to the absurdity of passing laws stating that you have the right to do something you already had the right to do. The same thing is happening today in Texas, where they are trying to amend the state constitution to state that you actually own your private property.
Well, in your view, then, it's OK to discriminate against blacks and Jews with respect to employment and housing. Afterall, in your view, freedom of religion and association is absolute....
Where does that leave the 14th Amendment?