To be fair, the constitution only says it was alright to own slaves because the south threatened to secede the newly formed county (at the time it was only the eastern sea board) so the other delegates were all like “crap! We just overthrew the British! If we don’t stabilize ourselves they’ll just come back and try to take over again” and allowed slavery.
The constitution allowed the right to bear arms in much the same capacity, as a means to stabilize a newly forming nation and allow for the means of self protection and defense that was prohibited under imperial rule, coupled with the capacity to form a militia should one be needed. Also bear in mind that the arms that the constitution directly refers to are wildly different in power and scope than what is common now