Idiots!
They are absolutely arms. Scary arms they want to ban, maybe, but still arms in the legal definition of things that are carried, aimed, fired and go boom!
Oxford dictionary:
arms
[ärmz]
noun
weapons and ammunition; armaments:
"arms exports" · "they were subjugated by force of arms"
Similar:
weaponry
firearms
guns
ordnance
cannon
artillery
AR-15s are scary because they’re not scary.
They are:
Ergonomic
Easy to train on
Lightweight (until you accessorize the crap out them)
Easily adjustable for different size shooters
When chambered in 5.56, unintimidating to shoot
Modular
Easy to maintain
Inexpensive
Blessed with a large aftermarket so you can build one just how you like it
From a civilian perspective, what’s not to like?
Leftist totalitarians hate them for these reasons.