If the BLM protestors attempted to storm buildings defended by the federal police that were deployed to those protests, they'd have been mowed down with light machine guns. Had the police not rioted themselves, nothing would have happened even if BLM had come to fight because it would have been abundantly clear that escalation would not lead to rising property values in Tokyo.

The Capitol should have been much better fortified by a much larger force given that the FBI, MPD, and Capitol Police knew or should have known about this plan for months. Had the presence of several hundred officers with multiple layers of fencing and visibly-manned M249 positions not been sufficient to convince their vanguard to run away, they would have been able to escalate to spotlights, LRAD, and less-lethal projectiles before needing to go with the real deal. A suitable amount of publicity for these preparations could very well have resulted in the Q Cucks Klan deciding to find an excuse to either make it a legitimate protest or call the whole thing off.

The deaths would have been at most two or three rioters, and possibly a few who get trampled in the panicked retreat. That would have been a light touch; it accomplishes the objective using a minimum of force, and if they saw reason nobody would even have been scratched. A medium touch would just be shooting anyone who tries to breach the perimeter until they stop trying (which would have been totally legal); a heavy touch would have happened to the BLM protestors if they had escalated to violence.

Kneeling in solidarity with protesters is fine because neither the protestors or the officer are breaking the law or indeed doing anything wrong. Letting an enemy force (and that's absolutely what a crowd of people with unlawfully-possessed guns and Army of Northern Virginia battle flags is) past your position is at a minimum conspiracy to enter and remain in a federal building without authorization.