Random Jottings wonders about why the Democratic Party is so viscerally opposed to ballistic missile defense —
Dems are less likely than Republicans to vote to spend money on a carrier, or a new tank. But they do vote for such things, they do accept the necessity of them. But they always seem to oppose missile defense.
As is usually the case with such things, there is no one cause behind it, but rather the confluence of multiple ones that come together to create the effect. The commentors hit on two of the reasons, sympathy for the Soviet Empire and desire for Planning, although in many ways the fomer is a consequence of the latter.
There is also a very strong reactionary trend in the MAL, along with a hefty dose of Luddism. BMD offends both of these sensibilities. I suspect that, related to the reactionism, is an unwillingness to discard moral equivalency. If the USA can protect itself from foreign missiles, that makes it different and special which is something that the MAL opposes in many other areas. One can see the same principle at work in disarming citizens (gun control) and making people like the VTech shooter just another victim.
It might also be that in MAL ideology, only victims are moral therefore a USA that defends itself (and is therefore not a victim) makes the nation immoral. Suffering is noble, not success, and missile defense is all about not suffering.
Beyond all that, there is the desire to not have the peons mess up The Plan, which also requires rendering them defenseless. The Democratic Party has enough sense to not apply this principle too strongly to conventional defense (although efforts at the death of a thousands cuts is frequently used, along with misappropriation of defense money to non-defense projects) but BMD is apparently just too much because of the confluence of the other factors.