OK, give me a chance. The thing is that I've found myself falling back on a peculiar definition of my own that sometimes helps me realise why people are disagreeing.
It is based on their blind spots. Socialists seem to me to have a blind spot about the abuse of power, hence the inevitable way that Labour governments eventually start restricting civil liberties - and how they fall back on centralised control in any given situation.
It isn't that they are convinced tyrants, or anything like that: they just don't see the problem.
Liberals are alive to the abuse of power at the core of their being, but they tend to be blind to the abuse of money. Hence their failure to come up with much in the way of distinctive economic ideas since Keynes breathed his last in 1946.
Again, it isn't that they are somehow bankers themselves, they're just not very interested in economics. They don't see it.
This is a rather roundabout way of writing about the strange story about the Paedophile Information Exchange in the late 1970s, and the involvement of the National Council for Civil Liberties (NCCL).
It is strange to grasp this, because of my youthful appearance, but I can remember the late 1970s rather well. Flared trousers. Three TV channels. Grunwick. Ah yes, it all comes flooding back.
I was a student at the time and into the more libertarian and anarchic causes, like joining the Liberal Party. They were the only MPs to vote against the nuclear reprocessing plant at Windscale, as we called it then - of course I had to join.
I remember the debate about PIE in student circles. I remember thinking it seemed very odd at the time, but don't remember much more about it. The truth is that I find it quite hard to fling myself back into the attitudes of the time.
I'm only writing about this now because Jonathan Calder was brave enough to do so, remembering the different atmosphere on the political left at the time - the psychological attempts to abolish "the very concept of childhood".
But my rule of thumb for distinguishing liberals from socialists is relevant here.
We are a far more liberal society, in many ways - I'll come back to this - now compared to 1979. As liberals, we have the advantages and disadvantages of that shift in attitudes. We are more alive to the abuse of power, and more blind to the abuse of money all around us.
We see child abuse now for what it is - the abuse of power. We have done so pretty much since the explosion of interest in the issue since 1984, or thereabouts.
But I have been wondering if this was relevant to the mistake that NCCL made at the time. The people in charge in the late 1970s, and now in the gunsights of the Daily Mail, were socialists and socialists have their own blind spots. The NCCL trio were clearly alive to the abuse of power or they wouldn't have been working for NCCL in the first place, but even so - I wonder...
It is kind of de rigeur at this point for columnists to add in a defensive condemnation of PIE, explaining - as if we needed to know - that they were wrong. And of course they were wrong, but it is interesting why they confused people at the time.
As Sam Leith pointed out in the Evening Standard yesterday, this isn't really about Messrs Harman, Dromey and Hewitt. It is about why society as a whole tolerated PIE back then.
So our collective shift from the naivety of socialists (blind to how power can be abused) to the naivety of liberals (blind to how money can be abused) is relevant here.
It isn't just the way in which a child abuse industry has emerged, terrifying parents who are not confident enough to resist, or the bureaucratic processes that get in the way of actually protecting children. It is the wider attitudes in society that manages to condemn adultery ever more fervently, that increasingly purses their lips at the way other people bring up their children...
I could go on. We all know society's new hypocrisies and train our mouths accordingly.