The idea that you can do so is pretty fundamental in politics. It's how the federal government justified the US Civil War, for example, and how the Founding Fathers justified a lot of things that tend to get glossed over in grade school history books.

The debate ultimately hinges on sympathies. For someone who wholeheartedly supports BLM, the riots might be regarded as something that was regrettable, but also understandable. In the words of Martin Luther King, "A riot is the language of the unheard." The observation also works in the direction of the Capitol insurrection. The rioters were there because they believed that their opinion on the election was not being heard.

Deciding which group had more grounds to be angry is left as an exercise for the reader.