are engagement rings necessary?

yesterday i had a lively discussion with friends about the ritual of engagement rings . are they necessary ? are they just as good if they are cubic zirconium?
i do think that engagement rings are an extravagance, but i also know that i would want to get one if/when i get engaged. i hate to admit it, but one of the reasons i would want one is because most women tend to get them from their fiances. i dont need the most expensive one in the shop, but i would like one. at least i admit it. and yes i would like a real diamond. i know its very materialistic, but i do feel this way.
on the other hand, i dont think that i would want a big blowout wedding. if i actually found someone i would want to spend the rest of my life with i would be happy. of course i say this now, but one never know when bridezilla might rear her ugly head. one never truly knows who may turn into a bridezilla.
what ifs are always fun to contemplate, especially when they are the occasional postive what ifs. usually im pondering worst case scenario what ifs.