They're immune to Fusion Cutters because otherwise Vampires would be invincible while attacking mirrors, and Viral Shredders would spawn something like two extra Shredders every hit, making them ridiculous. They're immune to Blade attacks because Cutlasses have a bad habit of instagibbing themselves on mirrors because of the 10x damage thing (no reflect needed!). That leaves Blade Spawners as the only ship that's unable to attack mirrors that should be able to, but that's a pretty minor issue, overall, I think. Just spam missile frigates if you see an incoming wave of Mirrors. Or, just sit and laugh as the piddly damage that Mirrors do fails to do anything about the forcefields over your command station.
