I thought you could choose? They don't have to be enemies.
That depends, could you choose not to be enemies with the Ogre charging at you screaming profanities while swinging a huge club overhead? If my theory is correct then I doubt you will have a choice as you wont be initiating war with the Empire, they will be the ones initiating war with you.
Lazy as in allowing people to make their own backstories. I think Todd have mentioned that they don't give you the backstory for that very reason several times.
Yeah I know but giving a reason as to why the PC is being executed or in jail doesnt necessarily screw up the backstory a player had in mind for their character, for instance no matter what in Skyrim your character will always be Dragonborn, having the player being executed for being the Dragonborn doesnt screw up the players backstory any more than what locking the character into being Dragonborn already does.