Absolutely do I support the troops. Might end up as one of them sooner or later.
About Afghanistan, I'm a bit undecided. On one hand, you have extremist lunatics doing extremely unpleasent things to people (and possibly harbouring more lunatics to strike at places outside their own state) and generally dragging the country into the dark ages. On the other hand, that bit was largely a consequence of the Cold War, with US meddling such that the Soviets wouldn't get a foothold, and then just abandoning Afghanistan to its fate and, as many are quick to point out, it isn't exactly the easiest place to get stuff done in.
To those who claim those who sign up are stupid/desperate for doing so, all I can say is that if they didn't, you and they would likely end up being drafted instead.
My main issue is, of course, with those who send others to fight (on both sides incidentally, how many of those mad preachers directing their resistance are actually on the frontline themselves? my guess is practically none), primarily because of the empty promises and violation of trust. It's certainly the case in the UK, where the much maligned government under labour has violated their side of the covenant with the armed forces, and abandoning returning troops without a care. I'm very surprised/displeased that Brown has not been a victim of 'friendly fire' on the few trips he's made out there.