It also implies that the person with the knife actually has a knife (not some Chinese knockoff Leatherman) and is physically an actual threat.
The fact is, a real cop, like they had decades ago, could have recognized this mentally-ill invert as no real threat, and taken him down with a blunt instrument of his choice. Unfortunately,
real cops are now a minority. Where men who could become real cops are hired, training ensures they will not become real cops. Every cop has to behave towards everyone they encounter like they're a 90-pound woman 'police' trying to take on a 300-pound muscleman and shoot first and ask questions later, because to do anything else would be discriminatory or call into question whether anyone but a hard man should be dealing with the high-conflict, low-information situations that police often do.
That is not to say that the pig shouldn't have blown this guy away. Any human should be entitled to blow this enemy of society away, regardless of whether they had swung the scissors out from their multitool or not.