"A preemptive conviction, if legally backed, would be justified in this case."

Preemptive conviction? In the US, the only kinds of "preemptive convictions" involve conspiracy charges...if you take some operative steps involving another person in a plan to commit a crime, then you can be charged and convicted of a crime. But you can never be charged or convicted of a crime simply because of what you say, what you write or how you believe (there are some exceptions, including crying "fire" in a crowded theatre or inciting to riot, but these are not relevant here). I can't image that British law (from which most of American flows) can be that much different!