HIT WHERE IT HURTS: Here's a war scenario that I have yet to read about elsewhere.

An Iraqi nuke on, say, Tel Aviv or New York would be bad enough. But a nuke in space could set the entire globe back to the communications dark ages (well, the 1950's at least) for several years. I'm not sure about residual radiation knocking out satellites over time (I've never head of that effect before, but maybe it's true), but the EMP could well knock out all the satellites that happened to be in line of sight at the moment of detonation. The loss of weather satellites alone could result in as many or more deaths over a 1-3 year "blackout" as nuking a large city - you might kill three million people at once with a nuke, but hurricanes and typhoons and tornadoes striking with little warning could rack up that many casualties or more, a little at a time. From an enemy perspective such disruption could be advantageous, as it would divert attention and resources to urgent civilian needs and away from the military. Not to mention the obvious and immediate advantage to be gained from knocking out communications, navigation, and observation satellites on which our military depends (assuming they aren't already hardened against such things).

So, how does this tie in with space settlement? Well, as someone (I forget who) pointed out several months ago in regards to space elevators, space infrastructure is very difficult to protect from military or terrorist action. Destruction of space-based resources can initiate a cascade of further damage due to its physical nature or the systems that depend on it.

Take the space elevator, for example -- as demonstrated in Red Mars, the sabotage of a structure of that size and extent would cause an astonishing amount of destruction across the entire planet (moreso on Earth than Mars, due to our oceans and thicker atmosphere, which would carry the destruction over even wider areas).

Large stations in LEO or MEO could present a similar risk, should a determined individual or organization find some way to deorbit them. That is an unlikely scenario, given the physics and resources involved --it's more likely that any attack on a manned station would be designed to destroy it outright, or to damage it in such a way as to leave the crew alive but in danger. The latter is more likely if only because it wouldn't require very good aim to achieve. Unlike an unplanned deorbiting, such attacks would have little material effect on our ability to wage war, but they would be a significant blow to morale and could very well divert attention and resources a critical time to emergency rescue efforts.

This is one of many reasons I have never been a fan of O'Neill-type colonies. They are fragile things by nature, which leaves them irremediably vulnerable to attack -- or to blackmail under the threat of attack. Surface settlements are much more robust, simply because they have a large body in which to hide themselves. Bases are likely to be built underground like bunkers for radiation shielding purposes anyway, and the ability to sprawl over a wide area means critical systems and resources can be distributed to better reduce vulnerability.

And of course, Mars in particular is safe because it will for a long time to come be impractical or unrewarding to attack settlements there.