I don't really understand the concern. The UK objects to suicide forums and American operators of suicide forums are protected by the First Amendment of extradition to the UK. So if you want to operate a suicide forum from America, just don't travel to the UK and you're okay.
a us person could travel to a country x and that x could send this us person to a UK prison? I don't know if doing so would be legal but when the rubber hits the road, each country x is technically sovereign and does not have to honor the first amendment of the US constitution.
So even if it might be frowned upon to extradite foreign (US) nationals in country X (such as Canada or India) to the UK, they could do it anyway to send a message?