This is definitely an interesting topic for which there is no clear line in my mind. Yes, in order to have actual free speech, the speech of people who hold positions you find abhorrent must also be protected. But there are certain positions that are considered so offensive that they are considered hate-speech. Some of those are clear and relatively obvious to most rational people, but for the most part, the line is pretty fuzzy.
And that line is shifting all of the time. It used to be considered quite acceptable to sneer at the queer community as being morally bankrupt, sub-human and an abomination. Although there are still people, and entities such as the Catholic Church, who vocally hold this opinion, it is becoming more and more widely accepted that this is indeed not just a difference of opinion, but is, in fact, unacceptable hate speech. Dehumanizing someone for how they were born is largely considered to be on the wrong side of civility and decency. But even so, the line is not entirely clear — but then neither are the lines related to sexism and racism.
So, what is an environment of normal, healthy differences of opinion, and what is speech that is so repugnant that it should not be tolerated? At this juncture, I think it’s still very much in the eye of the beholder.