As someone that has a strong focus on military history, I would argue that military history has no real benefit to the layman beyond casual interest.

Military history, when well studied, is more than battles, campaigns, leaders, and equipment. The full academic study of military history is how groups leveraged military power for the purpose of X or Y political and economic benefit. To properly study that, the researcher needs to immerse themselves in an understanding of the economics, politics, and social/cultural attitude of a people in a specific time. From there they can understand how and why Wars are fought and from there they move into how, logistics, military economics, doctrine, etc. For a layman, it doesn't offer much benefit to them as it takes more time than most people are willing to provide. It is how the famous myths come around of "German superiority" and "Russian waves".

As for the educational means, I would also argue against it. In a secondary school setting, history is meant to educate students in the ideals of their state and where they came from as a group. Studying D Day beyond the fact that it happened offers little to explaining the Experience of America, and it's something I never got when I was a young river counter. Far more benefit comes not from military history but rather social and cultural history, explaining how we got here as a society, not as a military.

I would argue that the lower a level you go, the less useful it is to the common or garden individual.

I mean, does it really matter to someone in life that when the Rangers finally made Pointe du Hoc that the German guns weren't there? Is there any practical use to knowing the relative technical advantages and disadvantages between the Panther and Sherman, or that HMS Dreadnaught made most warship designs obsolete overnight?

Assessing the Battle of Arracourt (1944) or US Army tank development in WW2 is of interest to many people, but as a hobby. It's of particular interest to me, as I'm a tank officer in the US Army, but I am hardly representative of an 'everyman.' in that respect. I see no particular benefit to mandating studies of battles and operations to the typical student, who is already short on time. If they -want- to learn, more power to them, but mandatory? Other than the fact that more people might buy my book and I get paid more, I don't really see much of a benefit.

At the larger level, though, when you start talking about politics and economics, more like the 'why' of warfare than the 'how', then, yes, I think it can. Why did Sherman march to the sea, and what was the point of burning Atlanta? What was the common interest of Prussia and the UK in fighting Napoleon? Why is Rule 1 on Page 1 in The Book of War "Do not march on Moscow"? Why are Vimy Ridge and Gallipoli considered to be defining moments for Canada, Australia and New Zealand in the concept of independent countries? i.e., military history insofar as it provides context to other events.

This is basically re-stating the previous answers, in that it should be taught (like everything else) when the military component of history is either significant in and of itself, or particularly illustrative of a larger phenomenon. Consider war in Clausewitzian terms - it is an extension of policy and an expression of state power.

Two good examples would be the rise to prominence of Germany and the U.S. over the last two centuries. The rise and fall of Germany as a power between 1866 and 1945 cannot be fully understood without accounting for their military proficiency, and the prominence of the military in Prussian history relates quite directly to the development and behavior of the 2nd and 3rd reichs.

For America, the strategic position of the U.S. (distant from the power centers of Europe and protected by oceans) played a important role in the rise of the U.S., and also the nature of American power. While the British Empire stood on naval power, America stands on naval and air power. This, arguably and in conjunction with other related political tendencies, led to the American model of "soft empire" - they won't always conquer and occupy, but they will hang of your coast and bomb you into compliance. But once again, Clausewitz warns us against military determinism - America is not necessarily a power because of it's fleet and air force, rather that America's inherent nature makes them well-situated to exercise those kinds of power.

The TL/DR is this - military history should be taught when it is historically important.

I would say yes, absolutely. If one of the purposes of public education is to prepare future citizens, then a basic understanding of how war affects society is essential. Understanding how military conflict has shaped society at every level is vital in understanding a nation's history and position in the world. A deeper understanding of who has served in the military will do more good than the endless platitudes of "freedom isn't free" or "supporting the troops," as will understanding the toll war has taken on veterans and communities.

To answer your more specific questions.

2. YES. Most academics are VERY liberal, which seems to go hand-in-hand with having very little inclination towards or knowledge of military affairs (though the level of hostility towards military personnel is, in my experience, overstated). Academic history took a much-needed turn towards social and cultural history in the 1960s and 70s, leaving many to think of military history (and, to a lesser extent, diplomatic history) was a fossil. Maps with funny lines on them and armchair generals judging the command decisions of long-dead white men in silly uniforms seemed to have no place in a field that now focused on the lives and problems of the poor and oppressed (and the structures that made and kept them so).

Military history has, of course, adapted, changed, and learned from the useful advances made by the rest of the field. Sadly, the "new military history," as some of its practitioners style ourselves, is not always recognized by our peers.

3. The causes of war are probably the most useful to understand. No one with a working knowledge of why the Mexican-American War started would say something this breathtakingly stupid, for instance. Giving a quick rundown of key commanders can be worthwhile, since all owe their positions to the politics of their time and many used their military careers to springboard into political careers. I would add on here a discussion of the the makeup and experience of the common soldiers of the army. Did the enlisted ranks reflect the demographics of the nation they served? Were they volunteers or conscripts? How were they treated by their officers and government? Knowing this will help illustrate socioeconomic realities and cultural attitudes of a period.

4. Depends. How a nation fought a war can become part of its national mythology (see: the US and the American Revolution, France and the Resistance), so understanding how important a particular war is in cultural memory and comparing that to historical realities can be useful.

5. I guess see my main answer above. Military history is not some bubble for reenactors to discuss. The military and war touches every single facet of society, and thus every style and approach to history can be done through a military lens.