Britain in the late seventies was beset by governments lasting less than the normal four to five years (one lasted six months) and strikes. Because of the politcal upheavals, perhaps, or simultaneously, younger people in general were more politicised than today and, more importantly, all people, paricularly those who weren't wealthy, were more confident of the ability to change things, contrasting sharply with the feeling of impotence today.
Whether the attitude, and consequently some of the lyrics, of the punk bands was merely a reflection of how many people felt, both in terms of their politics and their desire to change things, or whether some song writers helped to elucidate an outlook on life is debatable.
X-Ray Spex and Sham 69's respective lyrics were an attempt at commentary on life, the latter's concept LP 'That's Life' being the day in the life of a young man in East London. The Clash attempted to talk about politics, with mixed success, a task completed much more succesfully a couple of years later by The Specials, UB40, Killing Joke and Gang Of Four, although The Clash didn't initially have the luxury of having Thatcher's government as a target of vitriol. Stiff Little Fingers, from an observational perpsective rather than from personal experience, wrote about the war in Northern Ireland. Political lyrics were, of course, nothing new at all.
Demonstrative political action resurfaced in the late seventies and punk bands were often present at benefit gigs and gigs whose purpose was to raise social awareness. Who was using whom is also debatable.
The confidence of the ability to change things, mentioned above, was both the dominant contributing factor in inpsiring people to form bands, start independent record labels, put on gigs, write fanzines and was also the main visible usefulness of those activities. This confidence in the independent music business is the political legacy of punk.