[quote="drunkymonkey[quote:5e46a6214e]
I don't see why not really. It's going to stop him committing the real crime. I of course don't want some kind of Minority Report dystopia, but it's better to get someone before they commit a crime rather than after, surely?[/quote:5e46a6214e]

First of all, you were talking about suing, which has to do with civil laws - not crime, but damages. That is, whatever you did to me caused me to lose money, or the potential to earn money, so I want you to pay me for it.

If you're talking about criminal law, then how can you prove that someone intended to commit a crime? Are you going to arrest everyone who ever gets angry with someone else and thinks about beating the crap out of the them, even if they never do it? What if they say it out loud?

How do you prove *beyond a reasonable doubt* someone's intentions? There's almost always going to be some doubt about what another person is thinking.

What if someone prepares to commit a crime, and then at the last minute changes their mind and decides not to do it? How do they prove that? And then, what's the point of punishment as a deterrent if they're going to get punished anyway?

If someone is threatening someone else, has illegal weapons, or tries to hurt someone but is unsuccessful, then those are crimes themselves. The court can arrange for someone's safety, for example, by placing an order of protection. You can refuse to sell weapons to people. You can be arresed view child porn.

But you can only be arrested for what you do, not what you are thinking of possibly doing.