30, if not 3 years ago, this wouldn't even be a question. If somebody argues that the refusal is based on religious grounds, it seems like it would be a relevant test case in US politics.

Refusing to serve black people is illegal discrimination. It sucks that sexual orientation isn't a protected class in all states, but the bakers are legally clear here.

And the “but for” argument should have clearly applied here. They would not be denied a cake but for the gender (protected class) of who they were marrying. This was a clear case of judicial reinterpretation to meet an agenda.

Doesn't Colorado explicitly ban discrimination against gay people?