Muslims who have succeeded in mass murder for Islam.
Muslims who have attempted mass murder, but failed.
Muslims who were caught before they could mass murder.
Muslims who wouldn't mass murder, themselves, but support those who do.
Muslims who don't support the mass murder, but support the same totalitarian objectives.
Muslims who share the same general attitudes towards Islam, but are willing to allow others to not follow Islam.
Muslims who subscribe to some tenets of Islam, but not others.
Muslims who are nominal Muslims and whose value systems are more secular in nature.
the problem here is that the dedicated apologists only consider a very few to be "extremists", since they define extremism in such an extremely limited way, few fall under their designation. On the other hand, those who fail to distinguish between various Muslims tend to lump them all together. Both approaches miss the mark, because the former refuses to acknowledge the number of Muslims who share the same objective and the latter group fails to acknowledge the number of Muslims who don't.
As far as backing up anything people say, I'd suggest Pew reports. They have conducted any number of opinion polls in all sorts of Muslim countries including western European Muslim populations. Instead of shooting from the hip by either minimizing or maximizing, I think people should pay attention to them and acknowledge what they actually reveal.