I think the basic issue with 'arming all' is the escalatory nature of this, given that legislation might allow this, and where then it will be more about planning as to the outcome - having more firepower and quicker access, for example. Issues with this of course. And perhaps technology will do the same, like some aspects that have been suggested or are in progress - the technical means to only allow the gun owner to use the weapon and such for example.
But overall, one can't effectively restrict the weapons to the 'good guys', and a society where one might have to look over one's shoulder all the time is not one I would want to live in. Having travelled a fair bit, but not the USA, I have felt safe enough and mainly the only visible guns were seen in relatively poorer countries and by the authorities.
And it seems that guns are used more frequently in suicides, in accidents, or stolen, in countries where they are more available, so this alone is a burden that the non gun-owning countries don't tend to have. So I can't see how a more widely armed society could ever be more peaceful than one not having such.
Of course people will find ways to harm and/or kill others (or themselves) without such weapons, and this can happen whether guns are widely available or not, but this is hardly a good reason to add another means of doing so but rather as to making it harder for these other means to be used to any effect, given that multi-round weapons are often so effective at killing.