"Just like the debate over automatic weapons is a canard, since they're very rarely used in murders"
There is no debate surrounding automatic weapons, or, at least there isn't one on the national stage. Automatic firearms are dramatically different from semi-automatic firearms, and it's been a (specifically expressed) political maneuver to confuse/conflate the two.
The number of deaths attributable to automatic firearms is effectively nil, as they've been highly controlled since the days of Al Capone and his ilk.
When people are referring to "automatic firearms" in today's political arena, they almost always mean to say "semi-automatic firearms", which most closely maps to the sorts of weapon used in the Newtown and Aurora shootings.
It's a subtle, but important distinction, but as those who are trying to conflate the terms generally intend to do so to confer additional scariness to semi-automatic firearms that are simply not there.