There are a lot of reasons peace is better.
First of all, the battle plans never survive contact with the enemy. Civil War is the messiest of all wars, sometimes literally with neighbor against neighbor. And, as our Civil War showed, the maps which showed who sided with who could never be trusted. Would you want to be a Union soldier in rural Kentucky?—The map was not the territory.
Second, the scale of war and the variety of weapons are much much greater now. It could get way out of control and the results totally unpredictable.
Too many people here have watched too many civil war movies and think it is going to be quick, easy, and reletively painless to them because the other side is supposedly all filled with AIDS-infected gay dudes and hipsters that could never figure out how to fire a gun themselves.
Our civil war was a anomaly in the history of those conflicts. Those things typically go on for decades and won’t have a clean line of what side is where.