The Difference in US & UK Laws

I don’t understand the laws in the US, hardly surprising as I don’t understand them here either that well. What I don’t understand about the US laws is how come a prostitute can make false claims about a celebrity which are later found to be a pack of lies in a court of law.

The celebrity then tries to sue for defamation of character and is then told that because it had not been proven that the prostitute acted with malice so therefore she was only exercising her constitutional right to free speech. To cap it all she has now started a legal case against the celebrity because he dared to sue her.

All this is helping her achieve what her aim was in the first place, massive publicity. I'm almost certain this would never be allowed to happen here. The first amendment might give citizens in the US the right to free speech, but surely it doesn't give them the right to lie and profit from it?

Phil