Even as an American with no stake in the UK, this departure saddens me after how hard my family fought in Europe in defense of stability in that region.

The best thing that can come of this is that the UK promptly rejoins and everyone tries to put this indiscretion in the past. But even assuming they do rejoin, this tantrum has still significantly increased the risk of a massive conflict for probably a century or longer -- any hell-bent ideological maniac in any member state can now effectively use Brexit as a populist rallying cry that might actually work. (And most certainly, states with minority viewpoints will use it as leverage against the majority for an untold length of time.)

Aww, that's nice :-)