You ask for opinions on the slaughter of the Great War? Well, here's mine;
It was absolutely nescessary for those massive battles to take place. Yes, the casualty rates were appalling, but the ONLY way to win that war was on the Western Front against Germany. Germany being the most powerful of the Central Powers, it was only against Germany that victory could be achieved. Those morons in the British Parliament (First and foremost David Lloyd George) who were so adamant that the BEF should fight in other theatres to "knock the props from under Germany" and force her to surrender were delusional. Their only motive in this theory was to avaoid taking these huge casualties being inflicted upon the BEF by Germany. Examples include Gallipoli (complete fiasco), Salonika (Waste of nearly 200,000 British troops that could have been much better used in France) and Palestine where a quarter million British troops were wasted screwing around in the desert. (Palestine is in no way going to provide a decisive result against the Germans in France.)
It also has to be remembered that when the BEF was taking these ghastly casualties in France - they were serving a valid purpose, mainly sapping the German Army of it's strength. Let us also not forget that the French were completely exhausted by the Battle of Verdun and as a direct result of Verdun, led to the French Army's mutiny in 1917 in which over 80 Divisions flat out refused to take offensive action. This placed the onus of attack squarely on the British Army's shoulders. It was at the Battle of Third Ypres or more commonly referred to as Passchendaele that the German Army was broken. From this point on, the German Army was doomed to lose the war. They tried one last gasp with the Micheal offensive but it was doomed to failure right from the beginning. The same problem that plagued the Germans when trying to carry out the Schlieffen plan in the opening stages of the war came back and haunted them in the 1918 offensive. The German Army could only advance as far as the feet of their worn out Infantry could take them. They had no mass amounts of Cavalry to exploit gaps created, the Infantry advanced to quickly to stay in support range of the Guns, their supply lines were dangerously long and vulnerable, and lastly - the German Army never prescribed to Tanks in the Great War. (How ironic) Yes, they had the A7V, but it was not in large numbers nor was it very reliable.
Gen. Sir Douglas Haig should be regarded as one of the most brilliant General's in Britain's history. He never waivered in his resolve to defeat the German's despite taking horrendous casualties. The British had their fair share of incompetent General's, but Haig was not one of them. He did what had to be done to win that war. The huge casualty lists coming out of France in the Great War served a purpose. The causualty lists that came out of Gallipoli and Palestine were the tragic wastes because those theatres could not produce a decisive victory, but provide merely a sideshow from the main event in France.
Regards