Here's a blog post about how everyone hates each other over politics more than before. [And so on.]

So...I suspect my beliefs on this topic are out of step with the rest of LW, and even if I limit myself to the empirical aspects (i.e. set aside my normative differences) it's going to take a bit of effort to explain & justify my disagreements/doubts.

The first thing I notice is that the blog post talks about political polarization, as well as hatred/intolerance. Something I didn't realize until I glanced at the political science literature on polarization is that political polarization is multidimensional, so it's risky to talk about a change in political polarization in general.

To pin things down, we can first ask whom we're talking about: citizens in general, or politicians specifically? Then we can ask, polarization of what: specific policy preferences, or party identification? Finally, we can ask, is the polarization we care about variance in its own right (i.e. has the policy/party preference distribution spread out?) or covariance (e.g. has geographic sorting strengthened, which would be a rise in spatial segregation by political belief?) or attitudes between partisan groups?

There are therefore at least 2 × 2 × 3 = 12 conceptually distinct things we might mean when we refer to "polarization", and they have very likely changed to different degrees over time. There is clear evidence of decreasing inter-party cooperation in the US Congress, but this doesn't tell us much about the US public at large.

Even if we're clear that we're talking about the whole US public, not just politicians, much of the evidence adduced for polarization is consistent with multiple hypotheses. People often presume a null hypothesis that the public is pulling itself apart on policy, or that different partisan groups have more negative attitudes towards each other, but an alternative hypothesis I find plausible is party sorting: an increase in the correlation between party identification and policy preferences, which can take place even if policy preferences and inter-group attitudes remain constant. (The two hypotheses are not mutually exclusive, of course.)

Now I can finally turn to the evidence linked in the blog post. It links a National Journal article which talks a lot about Silicon Valley in the here & now, but much less about change over time (a line which leaps out at me is "Silicon Valley has long been a bastion of liberalism.", which suggests stasis and not change). The blog post also mentions Brendan Eich losing his job, which is one anecdote (and even if it weren't anecdotal, detecting a trend over time would call for two data points). Finally, it links systematic polling data from Pew, which I like. But with only one exception, every graph on that page is either (1) unable to tell us about trends over time because it only shows us results from 2014, or (2) consistent with party sorting.

Let's close in on the exception. (I doubt Pew minds much if I hotlink one figure.)

Because the charts represent responses to "political values questions" rather than something party-related, I don't see how party sorting can explain the widening of the distribution over time; this appears to be a parting of actual political views. Interestingly, there's very little polarization between 1994 & 2004; over that period it's as if the liberal & conservative sides of the distribution merely swapped places. Basically all the action happens after 2004, but even there the effect is not so great. The tails go from capturing 11% of people to 21%, not a negligible shift but not a radical one either.

I think the timing weighs against the idea that the Internet is to blame. Pew have asked US adults whether they use the Internet, and most of the change in Internet use happened in the 1995-2004 period (14% to 63%), not the 2004-2014 period (63% to 87%). One could tweak the Internet-polarized-people hypothesis so it better fits the timing, perhaps by invoking a decade-long time lag between Internet penetration and political effects, or by substituting something like "social networking" for the "Internet". But I would want to see an argument to back that up.

In a way this is all prologue, because you (75th) are talking specifically about "hate" between different political groups, and that might be worsening regardless of people's substantial political views. But I think it was worth warning about the multiple constructs lurking behind "political polarization".

I also hope I've made it less surprising that I believe the typical LW poster probably has an exaggerated idea of how much inter-partisan hate/intolerance has worsened. Worsened in the US, anyway, since that's the place I think most of us are talking about. (As Good_Burning_Plastic indicates, things can be different in different locales.) Given that actual political beliefs haven't changed much, it would be a bit surprising if the level of partisan hate had blown up. I have two more reasons why my null hypothesis is that partisan hate & intolerance haven't exploded.

One, I think of partisan intolerance as coming from the fact that political decisions can have big impacts on people's lives, so people feel strongly about those decisions and readily employ cognitive biases when thinking about them. Since this has always been the case, I expect partisan intolerance has been a constant fixture of political life, and the outside view leads me to predict only gradual & small changes in partisan intolerance's intensity.

Two, US writers have been making overblown claims of bottom-up "culture war" and such for years, so I now expect to see some Americans alleging unprecedented political polarization and partisan culture war regardless of the evidence. Some recent events do catch people's eyes and get brought up as signs that American politics is becoming unusually hostile, but when someone mentions something like the Brendan Eich incident, I have to wonder what the old baseline is supposed to be. Do the 1960s not count? What about the 1990s, when people were inspired to coin the "culture war" phrase? Or, if we want a more specific and more recent analogue, the Dixie Chicks kerfuffle?