OK, time for a karma beating...
If the USA wants to extradite him, it should be part of a mutual agreement. Currently the extradition agreement is biased towards the USA. Of course our last government did make that agreement but that's down to the fact that Tony Blair was Bush's bitch and we're still paying for the wars that the Bush persuaded Blair to drag us into.
Essentially the reasons most of us in the UK disagree with this extradition are (in no particular order):
1) The mutual extradition agreement is unbalanced in cases of this type.
2) The guy has Asperger's.
3) Your agencies essentially left the door wide open and he just strolled in. It wasn't persistent hardcore hacking (which your enemies are more likely to do)
4) He wasn't likely to cause any real damage - aside from potentially leaking information, which is quite serious of course but we've caught him, we can deal with him.
5) WE ARE YOUR ALLY! It obviously wasn't a UK conspiracy against the USA. You have plenty of enemies. Concentrate on them!