One side puts forward an argument, and the other side puts forward their argument, and a judge decides which is true and then applies the law.

Here the judge decided that he was at risk of death if he went to a US prison, the US was unable to answer that point, and the judge then looks at law - ECHR article 2 - to decide whether to send him or not.

The judge seems pretty clear that Assange should be in jail. Just not in an inhumane US jail.

Your comment BTW is a great example of how toxic these convos can be. I loathe Assange and I don't care if he rots in prison. You've assumed that I think he should be walking free.

To add to DanBC, a country absolutely can decide not to extradite to another country they believe plans to imprison someone at well below what they consider to be the minimum standard for human rights, the same way many countries do not extradite to a country that tortures or has the death penalty. There is a difference between making the argument “I don’t want to go to jail because it is depressing” and “the country’s planned imprisonment would violate my basic human rights and is to such an inhumane level as it would likely cause severe physiological damage”.