> You don't have to like the guy to recognise that the only solution is for the UK government to promise not to extradite him to the US.
No Country can realistically promise that when a request has not even yet been received. It's effectively putting your diplomatic relationship with another country at risk all to benefit one man, with no certainty of what the request is actually going to be.
If the US turn up and say "Him, he's a bit of a prick - give him here", then you'd feel more comfortable saying "yeah, he is. But no, can't have him from us" than if they turned up and said that some information he'd leaked had resulted in an attempt on the president's life, and he's being treated as an accessory.
Unlikely as the second one is, the point is that if you promise in advance not to extradite to the US, you run the risk of causing yourself a serious diplomatic incident because you have no idea how severe the charges are going to be in the eyes of the other state (or in fact their people).
That's why extradition requests are generally assessed on a per-case basis, and factor in the likely punishments.
Sweden couldn't possibly have issued a guarantee, and nor can the UK. It's a trope trotted out by Assange and his supporters to try and justify his position, when the reality is probably summed up this sentence in the article:
> wouldn't have guaranteed Assange's freedom outright
Unless he can walk out with a guarantee not to be arrested, much less do any time, he's going to stay put.