The appalling spectacle of Windrush generation immigrants being hounded and deported should help to dispel two great myths about politics.

Myth one is that racism is confined to the "white working class". Of course, some of these have backward attitudes which they express crudely. But equally, very many or more have lived happily with and alongside Windrushers. The harassment of them has been authorized by nice posh people who probably wouldn't dream of using "politically incorrect" language.

Racism is not just about words. It's about actions. In particular, it's about the actions of those in power. As I complained months ago, we hear too much about the racism of the white working class and too little about that of the ruling class.

Only a few days ago the BBC and other right-wing media were hyperventilating about the (yes, disgraceful) anti-semitism of a few idiots. They were doing so whilst ignoring a more harmful form of racism being conducted by those in office.

Myth two is the myth of perfectibility - the idea that it's possible to conduct a perfect policy with no ill-effects.

It is the case that most voters want immigration controls. As with Brexit, Theresa May interpreted this as meaning that they wanted a harsh and extreme version thereof. Hence her creation of a "hostile environment" for migrants: Ian Dunt and Stephen Bush are right to note that the deportations of Windrushers are the natural effect of this.

But this is not what voters wanted. They don't want Windrushers expelled, just as they don't want cuts in the numbers of foreign students. When voters want immigration controls, they are thinking of unskilled migrants and criminals, not French doctors, Chinese students or elderly Brits.

Maybe in theory it's possible to distinguish between "good" and "bad" migrants. And maybe some governments somewhere do have the ability to do so. But the UK does not have that ability. As Amber Rudd said, the Home Office "sometimes loses sight of the individual." (She'll be livid when she finds out who's running the department).

In practice, then, perfect immigration controls are impossible. This means we have to choose which mistake we make. Do we have a "hostile environment" which will hurt decent people? Or do we have a more liberal regime which will bring in some people voters would rather exclude? I'd prefer the latter. As I wrote months ago:

if you give power to the state it'll be misused, because the actually-existing state is a stupid bully. Just as "anti-terror" laws have been used to harass journalists and peaceful protestors, so immigration controls will hurt decent people. And for the same reason - because they are the softest targets.

The case for liberty is, in large part, that the state is not to be trusted with extensive powers.

It's tempting to conclude with some bromide hoping that lessons will be learned. This, though, is too optimistic. Politicians and the media rarely learn deep lessons from evidence.