It's OK - if your partner really wants one and somehow you can afford, go for it. If not, than don't. No point of complaining or badmouthing (or promoting) diamonds.

EDIT: wow, quiet a few downvotes (was expecting). Anyways, allow me to clarify --

I could go ahead and demonize chocolate (cocoa) or coffee (coffee farming is no field of dreams for workers) but more realistic approach is to see:

(1) The companies such as DeBeers have stopped trading (or at least try their best) blood diamonds

(2) Governments have banned blood diamonds -- at least countries like Canada has.

(3) Diamonds may be symbol of decadence and Masonite maybe the logical answer but you can argue same thing about wanting to drive an expensive sports car where a humble cheap sedan would do the job.

(4) People are complex - there are ladies who don't like or are against diamonds or they realize it is not worth the cost, etc. Then there are ladies who want diamond, PERIOD. Who am I to rule against them knowing there are people who want horseback riding or equally wasteful activity such as wearing designer shoes or buying the latest iPhone.

Point is, not everything is so black and white, right and wrong. There needs to be a fine balance and we should not follow a herd mentality in either extreme (criticizing or encouraging).