Then they should be forced to pursue a private prosecution in the UK, where the crimes were committed instead of relying on a technicality that allows them to wrest "jurisdiction".
Taking him in another country by force for what is essentially a civil matter is not ok. The process can take a long while, and all this time I assume he will be in custody - which most likely would not happen if he were to stand trial in his own country.
Plus yeah, we really don't like that he's being prosecuted for that. In all the talk about whether it's illegal or not it's too seldom that it's said "the law is just wrong". It protects too much the copyright holders, and the evidence that this is actually for the common good is getting sketchier and sketchier.