If they are predominant amongst agressors and victoms alike, that obviously cancels through.

My point is that it doesn't. Aggressors are the ones who have an advantage in combat, e.g., those who are stronger or have the free time to train. Guns reduce the "strategic inequality" between those in the biggest advantage in combat and those with the smallest.

Actually that is a very good point - is the effort really worth it in terms of lives saved? Possibly not... though the only alternative suggestion at the moment from the gun lobby is stationing armed guards in all primary schools, which to a non-US citizen sounds utterly desperate. Is the 2nd amendment really worth that much to you??

The issue of effort needed to force through an amendment does highlight a bigger constitutional problem: making changes is getting too hard. One consequence is that daft supreme court decisions then get set in stone. If you were going to spend effort on one single constitutional change, an amendment to make other amendments easier could be in order. A lot of European countries use referendums for amending their constitutions, which provides for stability against trivial changes, but still allows for amendments every decade or so.