Being from the UK I find the whole idea a little crazy to be honest. What does a 9mm produce? 400ft-lbs? I know penetration is key and that a slow heavy bullet penetrates far batter then a fast light one from a small rifle, but 400ft-lbs?!
We have five species of deer. The smallest two weigh in at about 30lbs and those are the only ones we are allowed to take with a rifle producing at least 1000ft-lbs. All the others need 1700ft-lbs. I guess it comes down the the shooter in places it is legal but it doesn't give you much margin for error and with a pistol you're far less accurate than with a rifle. I have no doubt that a skilled hunter could kill humanely with one, but the rules are there to (attempt to) stop stupid people from doing stupid things! They don't want average Joe taking potshots at deer with his Glock.
I know that some mention of pistols has been made in this discussion, but I don't think many would seriously consider using a pistol such as a Glock to hunt any sort of deer. I have seen a video several years ago where a fellow down South, perhaps in Florida, did just that... and the result was rather mortifying. He took 6 or 7 shots at a range of maybe 30 yards, might have hit the poor creature somewhere with most of those, but it took a rather long while to die and at the same time he was much too pleased with himself. It might have been a more merciful death had he walked up to it and whacked it with a baseball bat. Either the pistol's accuracy limitations, or more likely the shooter's poor marksmanship, resulted in holes from head to rear flank. Sad.
But 9mm from a carbine is somewhat different. The potential for accurate shot placement is significantly greater than from a pistol with open sights. Velocity from an 18.6" barrel, typical for a non-restricted PCC in Canada, is somewhat faster than from a 4.5" barrel on a pistol in many cases though it's not a radical increase in power.
I would really like to see how a 1,000fpe minimum requirement was established as necessary for hunting deer which weigh 30lbs. I've seen some silly regulations, but this seems among the silliest. Are these 30lb deer built with some sort of armour which makes them less susceptible to bullet penetration than, say, a coyote? A local here in the Fraser Valley has taken a couple of coyotes as part of his pest control business on farms with an airgun at around 100fpe. A coyote typically weighs 30 pounds or more, and these were smaller coyotes, but I've seen a couple right in the city which no doubt went over 70lbs. I'd not try such a shot myself with an airgun but if it were necessary, I can see using a .22lr for such hunting. Raccoons are rather tough animals weighing from 15 to 35lbs as adults, but are hunted with .22lr commonly and very successfully. An American friend of mine used to do just that with a Ruger MkII pistol, helping out a neighbouring chicken farmer when the critters were breaking into his hen houses and murdering 15 or 20 chickens apparently for the fun of it, eating little of what they killed. He said a single suppressed subsonic .22lr bullet to the brain was plenty every time. Nobody is getting 1,000fpe out of a .22lr pistol or rifle.
This stuff about requiring 1,000fpe or 1,700fpe for various deer types as a hedge in case of a poor shot, this bothers me a lot. If someone can't be bothered to learn accurate, consistent shot placement, they have no business hunting for living creatures. That kind of thinking, that a more powerful cartridge can compensate for sloppy shooting, that's just unethical. A gut-shot deer is a gut-shot deer, regardless of the foot-pounds of energy in the bullet which hit it. It's going to take a long while to bleed out, suffering incredible pain, and likely escaping quite far before dropping dead. The 'hunter' in such a case may never find the carcass. And such a 'hunter' is not likely capable of a follow-up shot to put the creature out of its misery, considering that the first shot was so far off the mark.
None of this is intended to make some sort of definitive argument to support the use of 9mm from a carbine for deer hunting. But sound reasoning AND the practical experience must be part of the discussion. There are many, many hunters who have, for well over a century, used .22lr for hunting deer up to fairly significant size. Single shot .22lr rifles have accounted for quite a bit of that. Surely a cartridge producing quadruple the energy of .22lr merits at least a serious discussion in this context.