I would say he shouldn't have started it, but in the position he was in, It doesn't look like he had much choice.
As for being "weak" in prosecuting the war, I think the real problem was the reluctance of the leadership to engage in a conflict many of them thought ill advised and detrimental to all concerned.
I think many of the early Union Army leadership, such as McClellan, didn't really want to fight with the South, and only did so reluctantly because those were their orders.
I think some of them suffered moral pangs about invading the South to stop them from having their independence.
Jackson would had no such problems.
The pro-slavery cabal in Rome orchestrated our civil war and they killed Lincoln.
I think you are projecting your thoughts on them. McCllen was an arrogant asshole who thought slavery was ok and didn’t give a damn if the union was split. Others thought no such thing and believed the Confederates should be crushed with no mercy for their treason. Thankfully Lincoln followed by Grant thought the union was worth saving, that slavery was the cause of the war, was evil and should be ended, and worked to accomplish both without totally destroying the south.