Criminals will get what they want. But if something's illegal, it becomes more difficult for an everyday guy who goes off the deep end to obtain. Also gives recourse to find the sellers and put them out of business.
I'd say armor-piercing bullets, high-capacity magazines and that bumpstock would be good candidates for "illegal." Would it "stop" anyone? No, but it would lower the risk. I also disagree with making "silencers" legal - if current hearing protection technology isn't sufficient, maybe the NRA should put some resources into that instead.
Security and freedom are always at odds and require a balanced approach to risk management. General statement, not weapon-specific.
NRA used to be for regular gun enthusiasts - judging from their latest commercials, they've become extremists. They don't represent the average person who just wants to go hunting or skeet shooting.