I am baffled at the way you post your initial argument to read as though the 'use' of 'mental illness' to explain a crime involving a Mslim is somehow the preserve of the 'right on brigade' apologists' - and this is then agreed with by another poster.
Just to be clear, this individual has a history of mental illness - I doubt he has gone to the trouble of incurring this in order to excuse his violence to cynical right wing observers several thousand miles away.
And if your comment refers to posters on this site, I refer yet again to my oft-repeated assertion that no-one, that is NO-ONE on here has even hinted at 'apologising' for violent behaviour by anyone anywhere ever.
If your slur is aimed at the wider world, then you need to make that clear, since your acknowledges stance on these issues would certainly indicate that you believe people on here to be excusers for this sort of incident.