Yes. At the core, some of these people are soldiers and not terrorists.
Even if they are "soldiers" rather than "terrorists", they are serving a cause that people should find abhorrent. The idea that slavery and beheadings for no other reason than "they pray the wrong way" are wrong is something that should be well-established, and that ISIS rejects the idea of basic human rights is well known.
They are not like regular civilians drafted into the 1940s German army, serving a country they may have been born into. Instead, they voluntarily agreed to join the fight, often traveling around the world to sign in to ISIS, all to serve a religious extremist ideal which involves harming others. The fact that they happen to wear a uniform instead of civilian clothes does not absolve them of that fact.