Erk, big question! The Reagan/US experience was different in the details, but broadly followed the same road and rationale. I'll cover the UK case as I live here. It's a huge topic, so I've probably summarised this poorly...
Thatcherism ushered in a widespread, total belief in materialistic individualism. Until the recession, anyway.
Not just the cliched Harry Enfield loadsamoney, or for US readers Gordon Gekko "greed is good" in Wall Street, and the rise of the yuppie, but the abolition of the majority of the post-war consensus. Thatcher herself seemed to have a genuine, but strange, belief that this would turn us all out like the little old lady mentioned in the GP. We'd have massive amounts of civic and social pride, whilst inhabiting a society where everything has been shaped around the individual alone, with competition for everything. Others in government were far more straightforward about the intended result.
Anything collective was bad. The welfare state, public housing, public ownership, public amenities were bad, as a matter of dogma. Even when they were good. That included tiny things like the council employing park keepers and gardeners, or big like providing enough public housing. You could buy your public housing, but the local council was not allowed to build a replacement or spend the proceeds on buying a replacement. Post-war, through the seventies, both political parties agreed, and even competed, to provide adequate public housing, public facilities, adequate regulation, an adequate safety net etc.
There was plenty wrong with the UK in the 70s, and some of the Thatcher changes were necessary. Just some. Unions were certainly overly powerful. Others, from the long term perspective have been remarkably damaging. It didn't have to be so brutal. It didn't have to go from safety net to now where we have a punitive, vindictive welfare system intended to punish and stigmatise. After 40 years of neoliberal policies to end state control and direction, local government is more centrally funded and controlled than it's ever been.
We ended up with individual insurance and pension schemes. Invest in the wrong scheme? Tough shit. The employer was divested of any responsibility to provide for their workers with a collective scheme. Not just pensions, but connections to the community, fair wages, wage differentials, job security. Billions in proceeds from oil or privatisations? Piss them away in tax cuts. Norway built a national investment scheme that's worth hundreds of thousands for each citizen. Collectivism is always bad.
As so often is the case, the right answer was somewhere between the two extremes.