But by starting in a prison, you're being restrained by a past. You were put in prison for one reason or another, whether or not you want to RP that.
That doesn't even make sense. Half the reason people don't want to start out as a prisoner is because they do want to create their own backstory, and not have to worry about fitting imprisonment in to said story. And saying that being able to craft every part of your character's story is "limiting" in any way, shape or form is ludicrous.