Whether political violence is warranted rests upon three factors. Firstly, one must consider if you are initiating political violence or simply reacting - which sadly is necessary. Mussolini obviously had instigated political violence much before.

Then, one must consider efficacy - if it's going to be useless then why bother?

Finally, one must consider the presence of altermatives. If you can at all avoid it, then political violence is not really justifiable.

In this case, the three elements converged, and it's in those cases that political violence can be warranted if done for good. This isn't even controversial, people defend the violence of the US Founding Fathers which engaged in much more violence for much, much, much less.