well actually they do say that they are unbelievers if they claim their muslim but try to advertise evil or lie about whats written in the quran or if they sin, repent their sin and keep sinning... idk where u got ur info about islam from but looks the same in christianity aswell... also in christianity sinning does not make u automatically a non-christian....

similar to catholics back before the reformation then the violence was directed at muslim jews and christians alike... just like isis... its like people got drunk of religion cuz they were so obsessed... religious extremism is in every religion... judaism, hinduism, buddhism and even atheism all have extremist examples currently going on today...

also the quran does not teach to hate each other... infact mohammed was allied with christian and jewish tribes back then... infact the quran even recognizes the torrah and the bible as 2 other holy scriptures from god (and the songs from david being another recognized scripture)...