In any given group, you can’t know with certainty whether past or future looters are present; looting is an action and not a quality. It is subjective.
Is removing anti-riot barricades ‘looting’ if protesters remove them from the street and out of the control of authorities in order to exercise their right to protest?
Branding someone a rioter empowers the utterer and subjugates the one deemed rioting in your framing. You seem to think it is justified to use violence against someone because of how you perceive their actions, even if they don’t hurt people, only property. There is a subtle but distinct difference. Using force to defend yourself and others has a long precedent and is largely uncontroversial in a public context such as this. However, a citizen in public generally can’t engage someone who is running away from them as they are not in imminent danger. Unless you think they are immediately returning with a weapon, you have to let them go once they get away or chase them and perform a citizen’s arrest. Shooting a fleeing person is frowned upon by the courts. Only police have that authority.
Why then are citizens taking it upon themselves to prevent looting and rioting? Defending businesses and private property from the inside and the entryway is one thing. Chasing fleeing ‘looters’ is a situation for disaster. Besides mistaken identity, which is already causing defenders and protesters who fought looters to be detained by police while actual looters escape, there are problems with armed individuals running into crowds of undifferentiable groups of protesters, looters, and rioters. How will the defenders know when to stop beating people up? How will they know if the protester defending the person next to them from collateral damage isn’t another looter? They will see what they want to see in the situation, on both sides.
Violence is not the way. I just don’t see how property damage is a mortal harm that justifies what I’m seeing. It may not be justified to damage the property, but as an individual or small group of defenders, there is no proportionality of response that makes sense against a large group of people. To start the fight is to lose on all sides. The protest will end when it ends. Lives shouldn’t end through protest, or through its consequences. One was enough to start this one. There’s a reason people do it, even if it may have knock-on effects. That’s the point. To shutdown protest because of its intended and unintended consequences is to make a means test for our constitutional rights. It’s not tolerated well in the streets or in the courtroom.
The defenders are unknowingly or knowingly participating in a counter-protest movement against the current legitimate George Floyd protests. It is being promoted through dog whistles by the right wing. It’s actually really obvious that authoritarians aren’t wasting this crisis. They start as many fires as they put out. I’m including rioters in that last part.