Who gets to decide what's useful and what metrics are employed to come up with that equation ?
That's simple; we do. There is no such thing as "universal" (meaning intrinsic) rights. Everything we do and decide upon is based on us getting together and (hopefully) coming up with well researched and reasoned opinion. There's no reason we can't do that with things like what's a reasonable "need" and what's a reasonable "want".
No Law abiding citizen has a use for a car to go over 110, no law abiding citizen has a use for fast food, no law abiding citizen has a use for alcohol or tobacco. Not one of those things hold a single bonified use or need for the law abiding citizen; and all of them, individually, kill vastly more Canadians than firearms. Yet they are all available for purchase and consumption without limit of volume.
If this was about public safety those would be tackled first.
First off, this isn't a zero-sum game. Just because we may not have placed reasonable limits on all the things that need reasonable limits doesn't mean we give up and stop tryin to be reasonable limits on
some things. So, yes, should the things you've listed be tackled? Absolutely. However, since we haven't done an adequate job of tackling them yet, does that mean we are morally obliged to stop trying to tackle guns until we are finished with fast food? No, we can do them in any order, and we can debate on what's more important.
Further, you focus on the 5-round limit and "volume limit" for the other things you mentioned, but fundamentally what we're talking about is "reasonable use" and "reasonable limits", and I absolutely DO think that we as humans and Canadians have the mental capacity to establish these reasonable limits, and I further believe the things you listed
should have reasonable limits:
There
are law abiding citizen that do have a use for cars going over 110kph: emergency services and race car drivers. As for your average citizen, I actually agree with your principle. The highest speed limit in Canada is 120kph, so let's make it a law that cars sold in Canada must have a governor that limits them to 120 (or maybe 130kph). That seems reasonable to me. Cars
are dangerous. It's already illegal to go over the speed limit, and cars are extremely regulated in both production and use (registration), so why make cars that go that fast?
Law abiding citizens absolutely do "have a use" for fast food. It's extremely convenient in a pinch, and in many cases (sadly) the price of value meals can be cheaper (and far easier) than buying and preparing healthy options at home. We have enacted laws to try and make people more aware of their unhealthy choices and to try and exclude certain harmful ingredients from food products, but it's really hard (and bordering on immoral) to go so far as to restrict people's access to the food.
Law abiding citizens absolutely do "have a use" for alcohol; it's entertaining, both as a social "tool" and for its direct effects on our mind. We have lots of laws regarding the use and consumption of alcohol. What more could we add that is reasonable? Maximum number of bottles purchased in one visit without an event permit or liquor license? Sure, as long we sit down and agree what that "reasonable amount" is, I'm game.
I will give you one: no law abiding citizens have any meaningful use for tobacco, other than to de-stress by satiating a craving for tobacco brought on my the use of tobacco which was useless and stupid to start in the first place. I think the whole world should follow in NZ's footsteps and ban cigarettes for
future generations.