ISIS is a movement involving thousands of official members, and millions of supporters. It cannot be dismissed as irrelevant to the religion itself, any more than Protestantism could be dismissed as "not really Christianity" when it came up with a different version of Christianity.

In both cases, they could be called heresies by "mainstream" Catholicism and Islam, but to claim they have nothing to do with the original religion is "a bizarre stretch of logic".

Similar to those who claim Stalin, Mao, the Khmer Rouge, etc. have nothing to do with "real Marxism". They were an extreme version of it, not something totally different.

While equating Stalin with Scandinavian socialism is unwarranted, to deny they are related at all is "a bizarre stretch of logic".