As I see it, the quran is not understood by most of us muslims because we do not read it for that. As for those who do they have so many misleading interpretations of it that it is very hard to discover what the quran really says for itself.
People do not even know how halaal and haram concept in the quran works. On top of all this we have so many people among us who simply are taking islam as if it is enemy of humanity thus giving islam the bad name.
The only answer to all these problem is education in general and critical islamic education in particular. The quran is all about tuning people sensible not stupid. Terry john like people are may be doing service to islam by showing many of us the mirror. This may help us wake up and do what needs to be done to regain respect for islam.
May Allah help us see his message clearly and help us guide others as we ought to.