No more or less than my rebreather is. Don't maintain your car, don't drive as you were trained, take hands off wheel, speed, drive under the influence, inattention, fiddling with your phone, lose control, mechanical failure (think breaks) end up dead/ badly injured (more likely to kill someone else too). Don't maintain your CCR, don't dive it as you were trained, old sorb, cells, not enough 02, inattention, you hurt yourself possible end up dead (much less likely to kill someone else in process) nothing to do with the rebreather trying to kill you all down to how you treat and dive the unit, attitude etc. It is just a silly statement that often get bandied around in discussion surrounding CCR.
Some people are just not meant to be diving CCR, some people should not be driving a motor vehicle.