There is no 'their mental illness' - it is our mental illness.
This is not isolated - this is another effect from a long standing cause.
Separation of any kind is the ogre we all continue to feed, whether it is Christians thinking they are righteously superior over the Muslims or the Muslims over the Christians.
It is Israel and Palestine, gay and straight, black and white, even men and women.
The greatest acts of hypocrisy are committed when any of us saddle up and ride our high horses of superiority or grovel in the gutters of our own self loathing. We must accept that each and every breathing soul is equally valuable or we are all pulling triggers.
Legislation alone will never repair what is broken if we first do not repair the thoughts about one another that brought us to the banks of this bitter river. Our condolences must be accompanied by our forgiveness towards everyone and to ourselves.