Clearly, McKinnon broke the law by hacking into these systems. Of that there is no doubt. But what harm did he really cause? According to the BBC, the Americans claim that he, “... caused $800,000 (£487,000) worth of damage to military computer systems...”. But what do they mean by 'damage'? It seems quite a loose term and one open to much interpretation when we're dealing with such ephemeral stuff as computer data.
More information from the Americans would help us clear up this very important matter. And that's the point. No specific information has been forthcoming – just accusations about some alleged 'damage'.
Did his crime warrant extradition? I rather doubt it but since the Americans have been so vague on the 'damage' he allegedly caused, we'll probably never know.