The focus on 'assault weapons' is probably a cultural one.

"Team pro AR-15" appears to have in part a mindset that the a powerful government if powerful against its people, not for its people. They seek to weaken this government by making themselves more powerful, albeit hoarding mere rifles is clearly an illusory attempt at it.

The less extreme part of "Team pro AR-15" seems to have simply developed a huge affection for warlike and automatic weapons, and the area of convergence seems to be the market for the 'tacticool' equipment that flooded the arms market after the appearance of the picatinny rail (and thus the realization that guns can be pimped by laymen, too). Same for "hello kitty" or generally pink-themed AR-15s.


Team "counter AR-15" doesn't see an actual use for such weapons except killing people. They don't have an affection for the guns and seem to prefer the modern European view that in a civilised country the individual gives up his armament (so for example doesn't carry a dagger when he enters a bar as was usual only 200 years ago even in European metropolises). They bet instead on being safer when others aren't armed to the teeth because the state has a monopoly on force and almost-monopoly on firearms. A conversion to this state is probably hopeless with about 200 million firearms in private hands, but the least tolerable threat -the 'assault weapons' - is a logical target for an at least partial implementation.
They don't stare at their own (non-existing)AR-15 as provider of security, but are scared by the others' AR-15s as sources of insecurity.


There also seems to be a rural-urban divide, with rural people having good reasons to not trust the timely reaction of government security officials in case of emergency and having good practical uses for firearms (hunting, self-protection against animals). Urban people meanwhile have emergency services ~ 5 minutes away (or could at least), not going hunting much but experiencing a lot of firearm-empowered crime (on their TV screen).
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I wonder why the U.S. got the crime and firearms thing so wrong. I've yet to hear about rural Frenchmen placing much emphasis on having semi-auto spitzer bullet carbines (and they're got some really lonely places!).
Quite the same goes for Canada; they don't happen to have such a huge conflict either as far as I know.