I've never understood why anyone would want to get involved in politics
I think the quick and simple answer is because that's where the power to change things lies. Most folk don't get involved, and prefer only to criticise, but I suspect one reason why politics is in the parlous state it's currently experiencing is because of the lack of involvement.
We tend to imagine that 'Government' is some sort of entity which exists in isolation from ordinary folk and whose main role is the removal of people's hard-earned cash through taxation. I've never really comprehended how national and international macro-economics functioned and was almost relieved when I discovered that I wasn't alone in 2008, when the world's economies played dominoes, but in democratic countries we do have the ultimate option. If we think that our government is taking too much taxation from us - the people - then we can become far more involved in politics than most currently are. It's precisely because most of us (and I include myself) don't want to donate large portions of our time to become active members of a political party and its subsequent selection processes that 'Government' can seem to be a remote, almost autonomous body.
Decent government depends on decent people getting involved for the long term. It needs good people who can ignore the pusillanimous, adolescent vitriol of the DFM and stand up for what they believe is right. Sadly, we're currently seeing the rise of the 'career politician', of which Messrs Osborne and Milliband are but two examples. We need more Mr Smiths going to London, rather than the current crop of finely honed, smooth talkers we now have. But that's only going to happen if more 'ordinary' folk get involved.