No, it isn't. DeBeers invented the 'tradition' in the 1940s through a cold-blooded plot that touched on every cliche villainy from viral marketing to child slavery. Prior to that the exchange of jewel-encrusted rings was uncommon and always rubies, sapphires and emeralds which - unlike diamonds that have an outrageously inflated price - actually are rare. On top of watching all of the big names of the day propose with a diamond, DeBeers also set it up so that diamonds would be symbols of love itself, and that "diamonds are forever" in an effort to eliminate the secondary market. And they got away with all of it too, because women like jewelry and men like to "keep up with the joneses" just enough for people to believe it's not completely phony.
Smirnoff did essentially the same thing to introduce Vodka to the western market. Except vodka has a merit, and a diamond is just a slightly more concentrated chunk of the material you are composed of. And Hallmark? Love may need a holiday but I think they could have done better than to celebrate a massacre with red disembodied hearts. This is the real reason why consumerism is evil: because everything becomes a parody.