SPAS 15 - The AR-Looking Shotgun that Frightened Lawmakers

It was the year 1986 when Franchi of Italy decided to make their new 12 Gauge shotgun look like an AR-15.
Like its older brother, the SPAS 12, it featured a dual mode of operation: it could work both as pump and semi-automatic, but while feeding from a box magazine, which is very uncommon for shotguns. But why is it?
And most importantly, what made this shotgun look so scary to north american lawmakers?

Thanks to Sport Guns Armory for providing the gun shown in this video.

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