I would say yes he should be suspended. You are referring to a video about a murder and then dismemberment of a human being. Clearly not okay to show to kids. It still stands, even in Canada, parental permission is dictated for under 18. These kids were underage. And I will firmly disagree with you Domino, it is not reasonable to make a sweeping statement that these 15/16 year olds were all "old enough to make their own choices." Chronological age is not a determinate, but regardless the laws clearly indicate that age is parent-dependent. If this teacher wanted to show this video, he should have received written parental permission, which I'm sure he would not have obtained.
As to de-sensitized, I'm not so sure. I have witnessed real death, real murder and nothing I've seen on television compares. There is just something bone-jarringly raw about knowing when something is real, witnessing true murder.
The sloppy beheading of a soldier, hands tied behind his back, as a serrated trench knife is thrust through his throat, the soldier's eyes opening wide as he emits a wet guttural yell that is cut off when the killer tears across the larynyx. It continues, the killer slowly struggling to saw through the muscles, tendons, ligaments and veins, until all that is left is the neck bone.
The man laying in the parking lot, his eyeballs dangling as paramedics attempt to put them back in the sockets, only to realize the sockets are now too inflamed, so they wrap the eyes carefully across his forehead with moistened gauze, only to be interrupted as he starts choking, a mixture of vomit and blood now blocking his airway. They quickly suck it out, check his vital signs, then thrust a tube down his throat, wrap his broken limbs carefully and rush him to the ER. The man was a victim of a jealous husband.
The 11 month old child, a small indentation on her forehead, laying in a hospital bed with tubes down her throat and monitors indicating no brainwave activity. You touch that little indentation to feel a portion of the skull collapse inward, the skin cold to the touch as this little girl is brain-dead, eyes intentionally left closed, although they're still slightly open and you see only the glistening wetness of lifeless white bulbs, all muted by the smell not unlike that of excrement from a dirty diaper, compounded by a stench of vomit and urine, as fluids slip from her little body.
Even the simple scene of a drunk motorcyclist laying on the ground, deeply snoring as the remnants of a 2" thick fence post extrudes from his exposed leg, along with a fractured femur that had pushed itself through the still-taut skin. And then your nose tells you what your eyes already see, a brown stain running down the side of his leg from his underpants.
These sights remain in your mind decades later. Longer if you know the victims. So no, we're not desensitized. We're simply being treated to a faux version of death in the movies, and thus posed to think we're desensitized. But, when we deal with real death, we're lost, confused, and we try to harden ourselves to no avail, because reality trumps fantasy and a 16 year old, mature or otherwise, should not be subjected to that, even willingly. They simply don't know what they're going to experience until they go there and then they just wish they never went there in the first place, but it's too late.
There is nothing desensitizing about seeing shows with fake gore and blood splashing the walls, it's just morbid entertainment and it doesn't compare to the real thing. This teacher should receive more than a suspension.