George III saw it that way, hence the war. In the end it is always war that settles such issues, its the guy on the ground taking and holding the territory of the enemy that decides things.
Nothing to do with George III. In the first place, he was a thoroughly splendid chap, loving husband, doted on his children etc etc. In the second place, he was going through a "personal crisis" at the time.
The American colonists were fighting against the Ministers of the crown. They were the ones trying to impose executive power without consent.