Yglesias says the lesson is that primaries test candidates and can reveal good ones. I think this is true. Insiders tend to not like primaries because a) they worry the more liberal candidate will win and be unelectable in the general election and b) if the primary turns nasty the candidates will essentially nuke each other in a mutually assured destruction campaign.
Point b) is a genuine concern, but I really don't think point a) is for the basic reasons suggested by Schmitt and in the post below.
