I'm an "average jock" (who has generally speaking no time at all for the SNP), however what I do understand is that the Scottish government released a terminally sick man (who may not even have been guilty) on compassionate grounds. I'm very proud to be part of a country that behaved in that way.
I hear what you say, though for me it depends on the individual involved. If we were talking about a person who repeatedly stated that he was proud of what he'd done, felt no remorse and was glad that so many people had died, then even being terminally ill, releasing him would not be an act of compassion, but a best an act of bureaucracy and at worse an act of stupidity.
Of course in this case we're not talking about such a gentleman, it's fairly probable that he may not be even guilty of the act that he's been imprisoned for, in which case any politically expedient method of releasing him was to be welcomed.