pr00ne,
As a British citizen I agree with your sentiment that the UK should try to act as a "force for good" (a phrase lifted from the UK military's mission statement, in fact). However, the reality is that last year's National Security Strategy only listed threats which directly affected our hard-headed national interest. Our force structures and funding levels have been based on its assumptions through the medium of SDSR.
Imagine if this had kicked off a few weeks later - perhaps post-PR11? We would have had no Nimrod R1, possibly fewer VC10s, possibly no GR4s beyond those committed to the HERRICK cycle, possibly no Typhoons due to lack of F3 cover at home, no HMS Cumberland...
I guess my point is that if we are going to retain this level of capability to perform forced interventions outside of the direct national interest, we need to state it in the National Security Strategy; after all, human rights abuses by dictators are far more common than many of the other threats listed therein. This would affect the priority applied to the relevant capabilities in our defence reviews - and would enable the appropriate arms to be funded accordingly.