I don't think there is any evidence of a 'serious' threat to the U.S. government from these sorts of things, at least not right now.
What we saw January 6 was amateur hour; yes, illegal, unacceptable, disruptive.........but not a material threat per se.
The organizers, thieves and persons committing assaults or vandalism should face the applicable charges (and indications are many/most will).
But I lie on the side of government being the representative body of the people; one which should be and be seen to be, accessible to them.
By all means, have an appropriate level of security, but no more than is necessary; with as as low a profile as is practical.
As someone whose regularly spent some time in Queen's Park and in City Hall over the years; I find even the current level of security marginally intrusive.
I would find an openly militarized environment more than a bit problematic.