Well, I've not really tried to define the term so explicitly, but I think it's fair to say that any position that is held by a majority of Republicans (or Democrats) is not extreme, because it would by definition not be outside the norm.
For example, public opinion in support of same-sex marriage in the US is currently at an all-time high of 64%, with 34% opposing. Being opposed to same-sex marriage is not an extreme position, as it is one that is shared by 1/3 of Americans. Only two years ago it was 42:40 in support. Therefore, the position statement "I believe that marriage should only be between a man and a woman" is not extreme.
The bottom line is that many views that are strongly associated with conservativism are likely to result in personal attacks if expressed in the aforementioned settings.
Just look at the flak Peter Thiel has gotten for supporting Trump. Why does donating to a major party's presidential campaign result in things like this [1]?
So can you do the ground work and show that a position like opposition to same sex marriage is actually frequently and casually labeled as extreme?
(I can think of lots of other invectives that people apply to it, I'm just not sure that it particularly gets treated as a non mainstream view...)
I also disagree with the point in principle. We even have a word for it when a majority gets on the wrong side of rational (and goes to extremes), a mob.
> So can you do the ground work and show that a position like opposition to same sex marriage is actually frequently and casually labeled as extreme?
I suppose I could, but I'm honestly not interested in doing so to support a casual conversation on a web forum.
> I also disagree with the point in principle. We even have a word for it when a majority gets on the wrong side of rational (and goes to extremes), a mob.
Actually I'm not familiar with the term "mob" being used that way, and a quick search doesn't seem to support your usage either.
Do you mean without regard to whether they are extreme or not or are you saying that no conservative views are extreme?