Not serving someone because of race clearly violates the founding principles of the nation of which the Constitution is to secure. We are all created equal, thus if one opens a business it should be for all. However, the Constitution does not force people to build ramps for the handicapped nor does it force the baker to endorse a behavior that he feels is morally wrong. The baker is not refusing to serve them, but rather, he does not want to use his business to promote a message that is morally wrong. This is entirely different and unrelated to the issues of the civil rights era and the lunch counter sit-ins. It is a distortion, by the way, that is intentionally fomented by the Left.
I have to disagree with this as well.
The Consitution served to limit the government. It defines what the government can do and what it cannot do. There is an understanding in the Constitution that in the eyes of government, all men are created equal (the lack of a ban on slavery works against this and was a tremendous flaw in a great document -- but I accept idea that the document sees all men as equal).
However, private business transactions are pretty much outside the scope of the Constitution. That document isn't about what businesses can do. It's mostly about what government can do (which is very little) with the understanding is that there is a great deal that government cannot do. And I maintain that telling a business owner who he must serve is not something that is covered in the Constitution.