Why we don't use the term 'daesh'
IS is a group of many people who have joined it independently after making a choice, although their choice seems an error to others, they have never stopped being 'people,' and we are all together, and all making mistakes, which if we have a competent larger society, our mistakes can be covered and we can be brought back wiser.
The term is used by politicians for political reasons, and even by news organizations, because it is derogatory. But like all terms of this type, it is dismissive and simplifying. It signifies the speaker is going to class these people as garbage and less than human and isn't going to think about them anymore as people.