"To keep up the pressure, the Germans began night raids, to stop the defenders repairing damage overnight. On one night raid, some aircraft bombed civilian areas of London by mistake; a mistake which was to become a crucial turning point in the Battle. Attacks on civilian centers were something which had been specifically banned by Hitler, who was still hoping at this time that the hoplessness of the situation would cause the British to sue for a negotiated peace. The German High Command knew that widespread civilian casualties would only harden the resolve of the nation to fight on. In reply to this accidental attack, the British bombed Berlin. Fears grew that cities would be raided more often, so children were evacuated again in a second mass exodus to places of safety in the country, as they had been during the Phoney War of 1939."

Quoted from The Battle of Britain -- The Official Royal Air Force Website

No one absolved Germany of being the aggressors in WWII. Only that the Germans did not indiscriminately attack British civilians until after the attack on Berlin. At that more civilians were killed in air attacks on Dreseden - 35,000 or Tokyo - 100,000 (or heaven help us on Hiroshima - 70,000 or Nagasaki) than in London - 30,000 - during the Blitz. Plenty of innocent blood to go around.