I think first past the post voting makes people vote for parties whom they only agree with on a few large issues out of a huge platform. People then spend a lot of time rationalizing their vote by reading/digesting opinions from their in-group, slowly transforming into a straight-line party voter.

That is a rational possible explanation.

If that were the case, then (in answer to the article), one would need just one liberal view that the highly educated can agree with (for instance, lower cost of higher education, lower debt on students), and then you would get the other views along with them.

No, you'd need one liberal view that you vote on. That is, the one view that you hold as more important than all other views must be liberal.

Or, you are like me (Libertarian), and many others who believe that a minimalistic government that only meets the needs of common defense, upholding court decisions and essential infrastructure are best on a number of levels. Most of us are also in favor of VERY high levels of transparency in both government and businesses in order to establish fairly open trade. Most of us would prefer to see transactional taxes over income taxes.

What consists of essential infrastructure is up to some debate, I might be convinced that education is, roads are, internet is (communications), electricity is... but not too much else. I feel that healthcare and other social welfare programs could lean towards family care requirements, which would allow for much lower costs for everyone else that doesn't have family for care.

I'm not hardline either, I'm open to pragmatic options for many things... but the direction should be towards freedom and not away from it.

I must hang around too many libertarians, most of the pro-gun people I know are also very much pro-choice and will even discuss total open border policies at times.

Oh yeah, there are plenty of exceptions. Libertarians being a large one. That's why I had to switch from "certainty" to "large probability" to "above-chance" when I was editing.

Are they exceptions, or do they just fall into the Libertarian category of prepackaged opinions?

Can't speak for everyone, but I am definitely more pragmatic than many hardline Libertarians... I'm okay with some government institutions remaining, as long as the direction is towards freedom from where we are instead of away. I'm okay with DoE, but would like to see more economically sound spending even if that means creating open options to compete with the incumbent publishers. That's definitely not a typically libertarian pov, but it's pragmatic in terms of lowering spending reducing complexity and something that might work and gain broad enough support.

Are libertarians usually for open borders? I hadn't heard this perspective.

It's a mixed bag, just like abortion.

FWIW, I believe the official platform of the Libertarian Party includes open borders.

I don't know if I'm an outlier, but my political opinions tend to match up with some supposedly liberal views, some supposedly conservative views, and some libertarian.

For example, I suspect overly generous welfare programs are corrosive, and I reckon abortions to be infanticide. But I also think it's insane to ignore environmental, labor, and consumer concerns just in favor of big-business's interests.

So I have to wonder: are people's views really so clustered as we imagine? And if so, would that stay true if the major political parties were unable to advertise for a few years?

You're either an outlier, young, or pay very little attention to politics. It's very difficult for anyone to avoid falling into the talking points of one party or the other these days.

I'm pretty much a level headed pragmatic libertarian... depending on the quiz, I've come up as centrist libertarian, communist or conservative libertarian.

I tend to not have many hard views, but lean towards options that lean towards freedom, while having a chance of enough populism to move in that direction successfully. Hardline actions rarely succeed in terms of getting into policy or law.

okay, we'll give you two years to find yourself, and after that you have to pick a side.

Jokes aside, it might be advertising, but I don't really know. I suppose if we consider news sources to be a form of advertising, that might be a reason.

Or rather, who does it best serve to perpetuate such a polarized form of political identity?

It strikes me -- based on absolutely no evidence -- to be self organizing rather than purposeful. Even if it was in someone's interest, and they were responsible, we would have to think about what the mechanism would be (political ads? social group pressure?)

Villains and heroes sell ads better than respectful discourse.