The white supremacists usually have a large number of firearms and actively use the second amendment. When aplied at other protests (see earty capital hill occupations) a similar response happens with police being more stand offish and refusing to take ground until absolutely necessary.
You’re right, but in most situations any casualties are unacceptable. The police will minimize their presence if they believe the people protesting have the conviction to use firearms against them. This is ehy the second amendment is so important, as defense for every other amendment against the corrupt and tyrannical.
I'm not American, but from my perspective, the modern interpretation of your second amendment seems to cause way more oppression than it relieves in practice.
Also, if there is a group of people with the "conviction" to kill other people with lethal force, that would be exactly where police should be getting involved.
Getting a bit off-topic, but since you brought it up I'd be remiss not to respond.
Your thinking is sonewhat correct. A group with firearms and the heart to use them would be a threat if the first response is to shoot. In most cases however the protest attempts to remain peaceful. Also, in many cases, only a small percentage have that conviction, but that small amount scares the police enough to keep them back.
The real irony is that the 2nd amendment is ineffective against a tyrannical government, and things that are effective (making bombs, molotovs, weaponized consumer drones) are pretty explicitly banned.