Why are the Berkshires in Mass so liberal?

[traininthedistance]

More like Vermont is an extension of the Berkshires. 

But, seriously, the Berkshires are liberal for all the same reasons Vermont is liberal, with the added factors that you have a lot of depressed postindustrial mill towns (Pittsfield, North Adams), and additionally a large sector of the current economy is centered around education (Williams), arts & culture, and tourism (Tanglewood, Mass MoCA, Lenox, Stockbridge, etc.).  I suspect tourism is in fact the Berkshires' main industry these days, and not just any tourism, but tourism of a specifically cosmopolitan bent.

[traininthedistance]

A cold climate does seem to have an liberalizing effect on white people

generally true but L.A. is pretty liberal.

Are there any non-Hispanic, non-gay, non-Jew, run of the mill white people there? A large enough population to make any sort of generalization anyway?

Most of West L.A./Santa Monica is fairly liberal and White, but this is more a factor of urban density than anything else.
It's true that small town/rural liberalism seems nonexistant in warmer areas, except maybe in parts of Hawaii, Asheville, and New Mexico. Am I missing anywhere else?

Nowhere that I can think of other than college towns, which shouldn't really count. Of course, that's misunderstanding cause and effect: The rural South is conservative because of its climate and thus its agricultural history, rather than the rural North being liberal because of its climate. (As the Plains and Mountain states show, being cold and inhospitable is hardly a guarantee of rural liberalism.)

Well, Montana is more liberal than Wyoming and North Dakota is more liberal than Kansas. 

It's not a guarantee, but it is a factor.  Perhaps it is mostly a factor of Scandinavian immigration, perhaps colder weather means more cooperation is necessary, perhaps it's more a matter of not being the South.  Perhaps all of these play some sort of role.