I think the bravery of standing muzzle to muzzle is mostly lack of imagination on the part of the field-grade (and above) officers. That was the way wars with firearms had been fought for 400 years--massed troops alligned and blasting away. They did it because the firearms, muzzle-loading smoothbore muskets, were so low-power and inaccurate that individual fire control was ineffective. The primary advantage of musketry over bow and arrow was that bow and arrow required lots of practice and highly developed skills. Muskets required a couple hours of training and you're good to go. Muskets were originally designed as a pike with a firing tube so that the soldier could take a shot at distance and then wail away with the pike. This evolved to the bayonet. Until the 1800's the bayonet was a more effective weapon on the field than musket shot, another reason why massed troops on an open field were the norm rather than exception.

But the firearms advanced faster than tactics in the 19th century. Mass production of rifled barrels and breechloaded weapons rendered massed troops on the field obsolete. So did explosive shot from rifled artillery. Unfortunately for common soldiers, most general officers didn't notice that change. A few did, mostly on the Confederate side. Nathan Bedford Forrest (my favorite general officer from either side) was one. He recognized that maneuvering of large forces was more important than massing. Same with Jeb Stewart and Jackson. One of Lee's greatest blunders was meeting union troops at Gettysburg and using 18th century battle tactics against 19th century artillery and small arms. Had the union forces tactics to match their weapons, they could've annhilated Lee's army instead of just soundly defeating it. But they were stuck with the wrong tactics, too.

Fortunately for the union, the confederates never acquired effective modern weapons. They were stuck with a collection of unstandardized smoothbore muskets and a strange mix of smoothbore field pieces.