Imagine an organization whose members are robotocists (robot designers & builders, AI programmers, operators, etc.) who refuse to allow their work to be used for non-peaceful purposes.
This may not appeal to all roboticists, but for those it resonates with, it could provide a supportive community and an awareness that they are not alone.
The Million Bot March is a protest akin to other marches on Washington, carried out by autonomous or teleoperated robots built by Robots for Peace members. The purpose is to raise awareness for the group, and to show people and industry that there are enough roboticists who believe in peace that it is not necessary to work with or support those who do not.
Of course leading up to a MBM, RfP bots could be used for other demonstration purposes, appearing a rallies, allowing human protesters to access demonstrations they could otherwise not attend, etc.
The march has a secondary value. It is a show of force that demonstrates that the time has passed where peaceful people can be oppressed through violent means. The march shows that the group can meet the enemies of peace on their own playing field, and that they can meet both the intellectual and physical challenges that have destroyed peaceful movements in the past.