>is that the other side will do it anyway and you end up dead.

Preemptive first strike logic[1] aside. This logic doesn't work because political violence never gets out of hand so fast that an entire political movement can be wiped out. On the other hand by starting/advocating for political violence you're almost certainly going to get the descent into sectarian violence before you can wipe out all the "fascists".

[1] Iran, anyone?