Harm reduction is not a single tactic. For gun safety harm reduction means requiring guns not to fire by accident, AND having gun owners take training that includes all the information about the risks that go up once you own a gun (especially to others in your household), AND requiring or encouraging gun owners to lock their guns up AND to store ammunition separate from guns AND ideally even to store them somewhere not in the house, AND reduce the number of guns in circulation.
When it comes to drug abuse, harm reduction can mean providing clean needles and other supplies to the user. The person isn't going to stop just because they're denied clean supplies. In the same way that you can't stop people from acquiring guns, but you can help prevent them from purchasing guns that are fundamentally unsafe to operate.
No, you literally cannot stop people from acquiring guns in the United States, as it's baked in the Constitution. Please make arguments based in reality.
I agree with all of the points you just made, and don't wish to be anywhere near a gun, personally. This does not change the fact that there are some people that feel the opposite, and will obtain a firearm regardless. If I can, I'm going to incentivize them to choose the safer option.
You should also consider looking in to the data about what actually happens to your chances of being shot once you buy a gun. It’s pretty stunning.