As Nadir says, its a balance issue. If "unrestricted capship warfare" were allowed then trade would grind to a halt, as traders would find better things to do with their time than get blown up at every jumpgate. And we would end up with a glut of pirates and terrorists, all stomping around Sirius in BS's and nothing less.
Its ironic coz every pirate faction needs a fleet of its own traders anyway, to provide necessary funds for their operations. Think how much more trading they would need to do if pirating in capships were allowed, and they ecshewed fighters entirely.
(BTW Templar I fail to see the relevance of the Nuremberg trials on this discussion. FYI Doenitz was not tried on his "unrestricted submarine warfare", since all parties agreed at the time that both sides did it. What's more Doenitz died a ripe old age, it wasn't like they took him out and hung him. But I find your defending Nazis and heaping sh*t on Americans particularly ironic considering you're from Polska. Bloody short memories....)