Your reasoning here is very similar to the rationale for oppressing Communist sympathizers during the Red Scare. They were opposed to the democratic principles of America and we ostracized them for it, and I'd thought the lesson we took from it was that we were very much in the wrong. I fully support gay rights, but I have trouble embracing what feels like a new form of McCarthyism (just s/Communist/homophobe/).

Hardly. There's an enormous difference between publicly ostracizing someone for holding beliefs or a political position that you disagree with and oppression. But there's leagues of distance between using speech and private choices (like whom to do business with) on the one hand and using the machinery of the government to deny people rights and to harass them at every turn.

For example, the KKK is horrendously ostracized in this country. And I think that's OK. But while they might be ostracized, KKK members still enjoy their rights, they still have the opportunity for free speech. And I think that's important too. I wouldn't equate the ostracization of open racism with McCarthyism and I don't think most folks would either.

The lesson from the McCarthyism scare isn't that ostracizing people for their beliefs is wrong. That's a valuable, even essential, function of society and an important aspect of free expression. Although we should definitely be careful in its use. The lesson is that hounding people for mostly private activities or activities in their past is wrong, and conducting public witch-hunts using the power of the government where the flimsiest of evidence is allowed to decide someone's fate is also wrong.