Anti-slavery evangelicals.

I'm not sure why this one seems included. Evangelical Protestants such as they existed in the 19th century were a major part of abolitionism. The only reason this doesn't completely work is that modern evangelicals as we understand them were different in many ways from the closest thing in the first half of the 19th century.

This does however seem like a potentially interesting idea overall. The animals-rights/pro-lfe example is particularly striking. Pro-life/pacifists might be another possibility.

One thing that is actually similar to this is how often people presume that coalitions in other countries line up in ways that match one's own. For example, one common misconception among Americans about Israeli politics is that the nationalist/Zionist sentiment is coming from the ultra-Orthodox(charedim), when in fact many of the charedim don't want a Jewish state at all and it is the moderate Orthodox who are strongly nationalist.