Please take a look at the linked article (and HN comments https://news.ycombinator.com/item?id=23385741) and note that the Federal "Kerner Commission, which was formed in 1967 to specifically investigate urban riots, found that police action was pivotal in starting half of the 24 riots the commission studied in detail."
Today we can see ample evidence of police escalating use-of-force (rubber bullets, tear gas, batons, etc.) on peaceful protesters.
If de-escalation fails with a large crowd in an urban setting and both sides presume violence with guns, how are police supposed to maintain control? Military tactics?
In none of the instant cases (the last four days of nationwide protests focused on or around BLM-esque causes) has it been correct for "both sides [to] presume violence with guns." Only the state agents could reasonably be presumed to have and use firearms. These protesters are not shooting at cops. There is no valid presumption there.