He objects to what he sees as government interference with the freedom of people to make choices, including, if they want, bad choices.

"It's not the government's business unless you are likely to harm another person," he says. "Harming yourself is your business."

Leyonhjelm is a libertarian: someone who believes that individual liberty is paramount and should be restricted in as few ways as possible.

The principle he invokes - that it is the business of government to interfere only when we risk harming others - is actually a cornerstone of liberal thought.

It's often called Mill's principle, after John Stuart Mill, the famous liberal, utilitarian and early feminist.

Mill thought government interference in our choices was oppressive even if that interference was genuinely for our own good.

Leyonhjelm agrees, though he also says as a matter of fact that we usually make better decisions for ourselves than the government would.

Most of us would probably agree that there ought to be limits on how much governments can interfere with our choices for our own good, and that we are often better judges in our own case than outsiders could be.

But agreeing with this much leaves plenty of room for debate.

How much interference is too much? Are there domains in which we are not good judges of our own good and might benefit from - even welcome - outside interference?

There's a large body of psychological literature on how good people are at making decisions that aim at their own well-being.

The record is not encouraging: people regularly make choices they think will make them happier but actually will not.

We have major problems with what psychologists sometimes call affective forecasting: we think we know how happy something will make us, but we're wrong.

This leads us to make bad choices with regard to money, in particular: people think that a pay rise, or winning the lottery, will increase their happiness, but if they're already comfortably well off, the money makes little or no difference.

And that's not because nothing can be done to increase our happiness: memorable experiences, for instance, do lead to increases in well-being. We also routinely make decisions we later regret.

For instance, in countries where there's no real national health system and no compulsory insurance - countries of the sort that Leyonhjlem wants Australia to emulate - people routinely go under-insured, and often pay a high price for it.

Part of the reason for this is that we tend to think of ourselves as much less likely to become seriously ill than we actually are. In terms of health, then, government interference may save us from ourselves.

While Mill's harm principle is very attractive, it may well be that it's psychologically unrealistic.

It was formulated at a time when optimism in the power of rationality was at its peak and scientific psychology was in its infancy.

We now know that we are less rational than we had hoped and that we often make better decisions collectively than we would by ourselves.

Many people who recognise that they are apt to make bad decisions in the heat of the moment take steps to prevent themselves doing so.

We impose restrictions on ourselves.

In a democracy, voting for a nanny state may also be a way of imposing restrictions on ourselves.

A minority of people may not like that, but that's just how democracy works.

So long as the restrictions are not unduly burdensome (how hard is to put on a seatbelt?) they don't have much call on our sympathy.

We don't want government interfering with our fundamental freedoms, even for our own good.

One of our most fundamental freedoms is to live in accordance with our own conception of the sort of society we want to live in.