Neither of us live in a country with a "constitutional right" to own or carry guns.
Which countries are you talking about?
Australia and the UK. In fact pick any country other than the USA.
We not only have the constitutional right--we, like everyone, have the human right.
Presumably the "we" you are referring to is the USA? You might not have noticed, but people from other countries also post on the interwebs, and they might have different ideas to you about what rights people possess.
Either way, human rights are just rights that groups of humans have agreed amongst themselves and then enshrined in law. Nobody is born with the right to posses a particular weapon.
Do you think you are born with the right to posses (and use) a Abrams tank, a cruise missile system or a thermonuclear weapon? If you don't (and you'd be a lunatic if you did) then we both agree that a civilisation should restrict which weapons it's citizenry should use, we just disagree on which weapons. Nothing to do with fundamental rights.