The great "Plan XVII" vs. the much-lauded Schlieffen one

A terrible plan!  Even though I just wrote a post giving Germany more crap for starting World War I and ruining the twentieth century for Europe, it wouldn't have been that big of a deal if the Schlieffen Plan (all in all, not a terrible plan) had succeeded.

It's a stretch to say that the Schlieffen Plan failed because it was altered at the last minute.  But it certainly didn't help.  Since the Schlieffen Plan relied entirely on the mobility and unstoppable might of a large force sweeping through northeastern France and encircling Paris, it was paranoia to fillet it, thereby severely hindering the chance of success on the Western front, in favor of defending from the Russians.  Not to get into the hypothetical game here, had Germany maintained diplomatic relations with Russia, the war could have been just another Franco-German conflict.  As it was, though, the Germans invaded Belgium, turned Britain against them, etc.

But why do I seem so certain of the success of the hypothetical Schlieffen Plan?  As it turns out, it was up against France's Plan XVII (described some here), which dictated, in what appears to be a horrible realization that France had no single technical advantage over Germany, that France's single best plan to repel the mighty force of the German assault was to run carelessly into the German lines, bayonets stained with Teutonic blood.  The Plan, predicated on the belief that all French soldiers were imbued with some sort of mysterious "élan vital" that made each Frenchman worth countless Germans, sounds laughable!  But maybe this élan vital really does exist, because it seems to have worked in repelling the Schlieffen-planned assault.