Several aspects to this that, for me, add up to "no problem here":

1. Space has always had a political element. The "politics of space" is a legitimate topic here.

2. Missile defense is certainly a space topic--it uses space technology and the more ambitious systems work beyond the atmosphere.

3. Space science can't be neatly compartmentalized separately from all other science. For example, most of the discussions here about Mars are discussions of geology. When we discuss the possibility of life out there we have to discuss biology. Seems to me that the only pure space science might be orbital mechanics...every other aspect of it overlaps with some terrestrial concern. Even rocket propulsion has applications within the Earth's atmosphere.

4. Discussion of the environment almost always combines science and politics. It's not so far removed from space science--think terraforming, and discussions of the possibility of other terrestrial planets. There's also the issue of whether we're destroying our own planet, creating a pragmatic motivation for building a dispersed spacefaring civilization. Every once in a while environmental concerns directly connect with spaceflight--concerns about use of nuclear power in space, concerns about rocket exhausts polluting the atmosphere, etc.

A bunch of bright and argumentative people can't be expected to conform to rigid intellectual boundaries. Looks like this thread veered a bit into purely Earthbound politics. Oh well...It got there step-by-step starting with a topic that was clearly space-related. Happens often, and I'm not going to lose any sleep over it. I try to avoid policing content, and it doesn't seem that the behavior resulted in flaming. Nothing here for me to worry about.