I think how to judge this attack depends on how the coin presents itself. If they're clear about being in a phase of the project where such attacks are feasible

I think how to judge this attack depends on how the coin presents itself. If they're clear about being in a phase of the project where such attacks are feasible then it's just vandalism, but if they're presenting a more flattering image of their project then demonstrating a 51% attack is a service to the public.