I've heard that there is an ancient (Jewish only?) custom that a soldier would divorce his wife and then remarry her after the war. Not divorcing one's wife could lead to a circumstances where the soldier dies, but the girl cannot marry another, which would then be a waste of natural resources from community's points of view and be quite sad.
So technically Batsheba is not married and hence marrying her is not a sin at all.
In fact, I am not sure what the big deal is all about.
Secularly, in ancient time, marriage is important mainly to decide fathership and inheritance. I do not think there is any confusion on paternity on who Batsheba's children is.
Uriah didn't end up inheriting his wealth to the wrong kids. David is a responsible father that inherit quite a lot for Batsheba's children. Hence, no victim.