Prove me wrong then
Starting off, Micah Xavier Johnson, the shooter at the Dallas BLM rally, was not in any way affiliated with BLM.
http://www.deathandtaxesmag.com/296207/dallas-shooting-suspect-micah-xavier-johnson-unaffiliated-blm/At a press conference, Dallas Police Chief David Brown said that Johnson, who had not been identified at the time, was upset about the recent killings of Philando Castile and Alton Sterling, and told the hostage negotiator that he wanted “kill white people, especially white officers.” Johnson was acting alone and not affiliated with Black Lives Matter, a group for which he also expressed anger.
So the shooter considering himself an "unaffiliated entity." But even if he did consider himself a part of BLM, that wouldn't link back to the roots of BLM itself because it's a movement, not an organization. Wikipedia defines BLM as "
an international activist movement, originating in the African-American community, that campaigns against violence toward black people." So unlike an organized effort with set-up goals such as the Nation of Islam or the Black Panthers, BLM is literally something anyone can just claim to represent.
But let's say by all means BLM is an "organization." Well, self-described "leaders" of the movement have already condemned the shooting.
https://www.twitter.com/Blklivesmatter/status/751311826013417472#BlackLivesMatter advocates dignity, justice and freedom. Not murder.
So, BLM is not an organization, but a movement with no true leaders (besides somewhat prominent individuals) or set agenda, simply a statement. And the claim by the petition that BLM promotes "the use of violence and intimidation in pursuit of political aims" is stretching the definition greatly, because the majority of BLM protests involve peaceful means of protest, with the examples used are several isolated incidents such as Ferguson and Baltimore where tensions between protesters and police reached their peak. Correlation does not imply causation.