Legitimacy. If you appear neutral in your descriptions, then when you say that their stated goal is to "usher in the apocalypse through conquest, rape, torture, and murder?", people are more likely to take that seriously and consider for themselves how to view them (and likely arrive at the obvious conclusion).

However, if you appear biased, then people are more likely to question the validity of what you are saying itself.

Good point, as are waffle's. Thanks.

They want to be called Islamic State because first of all it gives them legitimacy and it also helps with their recruitment because any action taken against them would automatically be called a 'War against Islam" which is exactly what they want to portray it as, they want it to be the West coming up against Islam. [2]

[2] https://www.youtube.com/watch?v=g4ouhpOPenI (Queen Rania And Arianna Huffington Discuss ISIS And What's Working In The Middle East)

Because you'll only have meaningful dialogue with someone when you use neutral language. If you were trying to convince an Islamic State zealot about faults in their reasoning they would close off their mind immediately when you use language like that.

Flippantly dismissing the Islamic State as an illogical death cult that just wants to rape and torture ignores their true aspirations and the legitimacy they draw from Islamic scripture.[1] To fight an ideology, you have to make an effort to understand it.

[1]: http://www.theatlantic.com/magazine/archive/2015/03/what-isi...

Islamic State is a term that has real meaning to many Muslims [1], referring to Daesh as Islamic State legitimises their caliphate.

[1] http://www.npr.org/sections/parallels/2014/09/12/347711170/i...

    > Why would you want to be neutral toward a group

For the BBC, at least, they're legally required to be.