I have heard a factoid often repeated that troops and commanders in the American Civil War were less willing to fix bayonets and charge to force a decisive end to an infantry firefight than contemporary or Napoleonic European armies. This is usually stated as being a reason for supposedly comparatively-higher casualties sustained in ACW firefights which would, according to this logic, go on for much longer and inflict more casualties than a decisive charge, which would result in one side fleeing.
Is this true? If so, was it simply a product of the fact that many troops and formations were relatively 'new' for parts of the war, or was it due to the way soldiers were trained? If it isn't true, where might the idea come from? I am aware that American troops were somewhat less willing to use the bayonet than British forces in the American War of Independence - does the idea stem from there?
I don't think it's true that casualties were lower or that American troops/commanders disliked the bayonet more than European contemporaries.
The European battles of Solferino in 1859 and Konniggratz in 1866 were both bloody affairs with casualties in the general range of an American Civil War engagement. Waterloo had perhaps more casualties than a typical American Civil War battle. So whether or not the bayonet was employed, European battles were not particularly bloodless. (What's different about these European battles is that they were decisive on a strategic level, and resulted in a prompt armistice.)
As for tactics, American Civil War officers generally attempted to emulate European tactics and drew their equipment and battle tactics from European templates. On occasion, European trained officers like Franz Siegal commanded units directly. While precise statistics on how many bayonet charges were ordered (compared to volley fire) are unavailable there isn't much evidence to suggest that these were more common at Sofierno than at Antietam.
While the increase in firepower of the Rifle-musket and Rifled artillery over Napoleonic counterparts has been exaggerated, there was still a meaningful increase in overall firepower by American civil war units at middle and longer ranges compared to Napoleonic conflicts. By 1866, one year after the American Civil War ended, the bayonet charge in Europe was fatally undermined as a tactic by Prussian breachloading rifles at Koniggratz.
Source: Nosworthy, Brent "Bloody Crucible of Courage: Fighting Methods and Combat Experience of the Civil War" 2005