Oo, I'm so going to regret this, but I'll have one attempt at answering all the questions (and not getting offended by the coarseness

).
Let's start with the biggie: capitalism. I can only speak for myself, but it's pretty clear that capitalism and corporatism (and a theory of value based around profit) are the root cause of pretty much any problem you can name. PS is not an anti-capitalist group: our purpose / terms of reference / call-it-what-you-will is to tackle aviation and its impact on climate. However doing that means advancing a message around endless economic growth ("ideology of the cancer cell"), people before profit (i.e. Sipson and its inhabitants over BAA and its shareholders - or the right to not have aeroplanes over head every minute or so) and the clear class issue that is the myth of cheap flights.
Put another way, we used to demand (we have these demands, they shape what we say and what local groups ask) a tax on aviation fuel. We stopped demanding that, because it was seen as a state intervention (not in the Libertarian way): i.e. asking the Government to do something instead of doing it for ourselves. Read our blogs to get a better idea of individual activists' political beliefs.
Cheap flights are several things. One thing they are not is a great social liberator. What they've enabled is the wealthy to fly more than ever before. Check out the Sustainable Development Commission's research (
http://www.sd-commission.org.uk/publications/downloads/AviationandSocialExclusionData.pdf): In 1987 4.71m people from social groups D/E flew for leisure (13% of flyers - table 7). In 2004 9.26m people flew for leisure, down to 10%. For people in social group C2 it's 7.82m to 15.5m (22% to 17%). Not bad... until you look at social groups A/B: 11.93m (1987) to 30.95m (33% to 35%) and C1 (11.76m to 33.56m - 32% to 38%). So although more people from the bottom three social groups are flying, this is dwarfed by the growth in the top three social groups, and the person sitting next to you on a plane is now more likely to be posh than in the 80s.
Second homes in Majorca are more of a problem than a summer holiday in Malaga, but for fuck's sake: the climate is changing, it will affect the poorest people around the world first and worst, and in that context I don't think anyone - working class or not - can justify a stag do in Prague or a shopping trip to New York. Let alone flying to a business meeting that you could have done by phone but wanted to feel important and earn some air miles.
When we started on aviation, no one was saying anything about it. It's 13% of the UK's climate impact! Energy was covered (FOE, Greenpeace, WWF and people taking action against nukes and coal) so we focused on carving out a new front. I'd say it's been successful: Stansted probably won't expand and Heathrow definitely won't. We judge our success by CO2 emissions stopped, attention drawn to an issue (five of us dancing about on the roof of Parliament didn't stop any CO2 but it did expose the corruption between BAA and the Department for Transport) and how many pints we get bought in the pub afterwards.
Our media people tend to sound posh because they're mostly uni graduates or students who have had training in speaking clearly and succinctly while chained to a runway at 4am and getting shit from TalkSport journalists. There's also an element of self selection: it's those who put themselves forward who do media, we don't make people, and people from uni or public school tend to put themselves forward.
Oh, and I haven't flown since 2002 - and my family all comes from far, far away, so I don't see them much. I don't think we can justify flying when we are telling others not to fly as much.