Neither side knew what they were getting into but the planned German offensive had to be stopped. Technology had outpaced tactics and a stalemate was inevitable. Haig was a dud but no-one expected the attritional campains. The British land forces, although well-trained career soldiers, weren't large enough and Kitcherer's huge volunteer army was trained. Conscription started in 1916, once the general enthusiasm had waned. The discovery that over 50% of eligible men were not physically fit enough to pass the rudimentary health checks was a national scandal and led to huge social reforms.
Although kings may not directly kill kings, George V refused sanctuary to his cousins, the Romanoffs, and allowed them to be murdered. Even though we were on the same side.
Prince Andrew went to the Falklands and by all accounts was bravely kept out of the way of anything with moving parts and young Harry heroically used long-range missiles to kill 24 Afghans (some of them probably were kings as those are ten a penny in the area.
I think I'm probably agreeing with you. I'm just trying to suggest that there weren't the subtle political/class motives, just ignorance and incompetence.
As Kipling's suggestion for a war grave epitath reads "If anyone asks you why we died, tell them: "Because our fathers lied."".