...a system of ideas and ideals, especially one which forms the basis of economic or political theory and policy.
It is for this reason that ideology is important yet it has become something of a pejorative term - I recall someone upset by my thoughts on public health sending a screaming tweet: "Ideology, ideology, ideology" it said, as if I would be upset by my observations being basis on a more-or-less coherent set of thoughts.
We have arrived at the point where, in the minds of too many, there are two distinct positions in any debate or discussion - "ideology" and "evidence-based" - where the latter is deemed to be superior. The problem I have is that, without a premise for your proposal, prescription or policy, any amount of evidence won't necessarily tell you that it's the right (or wrong) thing to do.
We're told - repeatedly - that alcohol can be damaging to our health. I'm guessing that nearly all adults and most children are aware of the risks (although not necessarily how to assess or quantify those risk) involved in drinking. Let's assume that some evidence is presented showing that, if we increase the price of drink, then consumption will fall and fewer people will damage their health as a result. Indeed, since there's lots of evidence that increasing price reduces consumption, we could apply the evidence to any activity or product that has negative social consequences.
The point isn't what the evidence says but whether we should enact some policy on the basis of that evidence - is it right to make booze more expensive for everyone because a small number abuse alcohol? This isn't a decision you can make on the basis of evidence, it can only be made on the basis of ideology - a premise that says all population intervention in personal choice is justified on health grounds. The evidence says the decision - putting up the price of beer - will have a positive impact on health but the decision to restrict choice (for that is what a price intervention is) is ideological.
As of course would be the opposite decision - not increasing price because personal choice trumps public health.
Our public administration has adopted an ideology that needs, in the interests of democracy and freedom, to be challenged. Yet whenever a challenge to the premise (essentially that government intervention is always justified) is made, the response isn't to present a logical rationale for that ideology but to gather together "evidence" showing how government intervention is a good thing. "What matters is what works", as Tony Blair would have put it.
The result of this outlook - a sort of anti-ideology ideology - is a sterile debate conducted on the basis of fact-checking, appeals to (evidence-supplying) authority and attacks on the critic for basing his argument on 'ideology'. The irony of this is that debates between, say, Marxists and libertarians are more honest and interesting than the faux-debate that dominates much of our current political discourse.
Take a look at the debate over Scottish independence. The Scottish government under its Scottish Nationalist Party leadership has produced a vast tomes setting out the "evidence" for independence with the emphasis on the economic case. And those opposed to independence have, likewise, set out their case for retaining the United Kingdom.
However, the argument isn't about the economy at all. Nor is it about the welfare state or the army or nuclear bombs or any of the other aspects of the debate. The argument is ideological - should Scotland be independent or not. And the voters will, in the main, make their decision to for 'yes' or 'no' on the basis of this ideological debate. Or rather on the basis of an ideological debate that simply hasn't happened because we've forgotten how to lift politics out from the banal and pragmatic and into the realm of ideas.
Accusing someone of "ideology, ideology, ideology" isn't an insult, that base of ideas allows us to make policy choices where the evidence doesn't direct us to a choice - the world of macroeconomics is filled with such choices, for example. And ideology provides the basis for these choices, big and important choices that affect everyone's lives, to be debated and discussed.
Ideology really does matter and we should use it more often.