The fact that "Islamism" is the message of the Koran and it is perfectly reasonable to assume, in the absence of conclusive evidence to the contrary, that anybody who defines themselves as a "believer" in that book as the divine world endorses the message of that book 100%.
On what do you base your 5% figure?
Years and years of being a Muslim, scocialising with various Muslim communities, attending numerous madrasahs in 3 different countries etc... you know actual real-life experiences.
If you think 95% of Muslims have ever even read the whole quran in a language they understand you are either ignorant or plain stupid.