I think the difference is sympathy for the future victims. Some people would prefer a murderer be stopped, rather than continue their life in prison murdering other inmates and guards, or being released and murdering innocent/productive people.
Whereas some don't care how many people are murdered as long as it's not someone they care about, and as long as they're innocent.
"Three innocent women raped and murdered by a guy? Well, that's the breaks. What? You want to actually stop the guy? You inhuman monster! Life is precious!"
It lets them feel good that they "gave him another chance," and doesn't concern them that giving him that "chance" will result in numerous innocent people permanently losing their chance.
Personally I think all murder convicts should be released to the custody of the sentencing judge after release. If you're comfortable leaving your wife and children with him, then he can out. Most judges (and rich white liberals) know it's not their neighborhood the murderer will be hitting up, he'll just be killing some poor black people, so who cares, eh?