Why political tribes are becoming more dangerous than ever

Ideological coherence is a sound political strategy. Elections have single winners. Since elections are multi-dimensional, you need to form a coalition to be that winner. But the tighter you make that coalition, the less you have to compromise while still winning.

Sure, it's intellectually bankrupt, but what would you rather do: be right, or win elections? The latter choice always gets you nothing -- at least when faced with somebody else who would rather win.

It seems like this tradeoff was just sitting there for decades or centuries, but we only started implementing it in the last 40-50 years or so. I wonder why it took so long.

The straightforward answers would seem to be something like "intellectual honesty" or "human decency", but I really can't imagine a time when that was widespread.