It's pretty clear the difference isn't the presence of guns, or the "restrictions" (in Brisbane you need a licence that boils down to knowing gun safety), it's an attitude. The attitude in the US seems to be it's perfectly acceptable to use a gun for self defence, up to and including killing someone. In the rest of the world we are happy to delegate killing people for crimes to the government, so under no circumstances is it legal to threaten someone with a gun, let alone shoot them. Accordingly the rest of the world's population is happy to have fairly mild restrictions on gun use that allows their use for anything (sport, farming, game hunting, ...) bar personal protection from other people.
I suspect the person you are respond would disagree violently on this one point. To them the entire point of owning a gun is self defence. They insist they must have the right to kill someone.
Moving to Australia and realising I didn't like to live life with 'my head on a swivel' was quite a revelation. And the laws around proportional use of force down here are a refreshing change to the 'shoot the person and drag them in your house to claim self defense' American mentality. You'd end up being charged with murder doing that here, and rightfully so imho.