It really wasn't. The Colorado law did not disallow making gays a protected class, like blacks, Jews and women. The law required refusal of government services to people who identified as gay. For example, a gay book club couldn't meet in a library. A gay bowling club could be denied the use of a community center. The real fear was that, down the road, city-owned hospital could deny treatment to gays. "This Colorado cannot do," Sandra wrote.
Where in the Constitution does it state a citizen has the right to rent someone else's property or work for a private business? It doesn't. The law was perfectly Constitutional.