Colonizing the moon and mars would lead to speciation because of the effects of reduced gravity, I would imagine. That said, lunar and martian babes will likely be hot if they stay in shape. Think about the effects of low/no gravity, and no sunlight on aging--35 year olds will probably look 20.
At some point, there will definitely be an us/them feeling as the culture and needs of the societies diverge.
Having said that, I'm with you. 'Arms Races' and War often support great technological leaps that ultimately benefit humanity (think plane engines or superglue) - wouldn't it be nice to see a space colony race where nations and corporations invest in new technology to support life on the moon, on Mars, and ultimately here on Earth, without the motivation to kill people first.