30% of the population holding extreme views isn't the same as any particular view being held by 30% and considered "extreme". They don't go into exactly what this figure means, but at the least we can imagine 15% of Americans holding one extreme and 15% holding the opposite extreme. Or even more credibly, it could mean that 30% of people hold at least one "extreme" view, but each individual "extreme" view is only held by 1-2%.

I believe the graphic just says that 30% hold some view that is extreme, not that 30% believe the same extreme thing.

Disregarding the article's intent with that statistic entirely...

A) a "population" can be 1 person, a random demographic, a continent, or a fringe religious group. It just means a mathematical set of people.

B) while one could argue for or against universal moral truths until they're blue in the face, from a practical standpoint there are absolutely views that large populations believe in that are objectively abhorrent. FGM, killing people for their religion, torturing immigrant children, etc.

Perfectly normal, perfectly healthy in Illinois [1]

1. https://www.chicagotribune.com/politics/elections/ct-met-ill...