The mass murder example is a counter point to the (implied) argument in the grandparent that "[getting] the attention of an incredible number of people very quickly" is the same thing as an effective protest.
It is possible to get lots of attention for your action without that attention translating to support for you or your cause.
The parent continues to discuss how they believe there was damage above and beyond "wasting the time of a bunch of build cops" and explicitly states what they think the damage would be.
Perhaps choosing a different example would have been more tasteful, and may have avoided this side discussion and being flagged to oblivion, but it did not ever claim the two events were equivalent.
It's possible that the mass murder example, while not directly compared with the original action, is implied equivalent by the mere juxtaposition of the two but I don't think that was the parent's intent.