I guess I don't see wearing diamonique or CZs with my real diamonds as any different than wearing a Target t-shirt with Manolos. Sure, Target probably sells the same white v-neck 3/4 sleeve T as Saks does, just with a different label, but that doesn't mean it's wrong to buy the cheap one, and even to wear it with your $200 jeans, $800 shoes and $2000 bag.
I also think that, in general, the conversation is exactly opposite with natural vs. man made diamonds from what it is with real vs. fake bags. They aren't making (as far as I know) CZs in sweat shops. Lives are lost because of "blood diamonds." I am completely against companies/individuals selling CZs as "natural" or "lab grown" diamonds when they clearly aren't, because that's dishonest and illegal, just like it's dishonest and illegal to buy and sell fake bags. But I personally don't have a problem with a $25 pair of CZ earrings, as long as the buyer is aware of the facts.
Like a previous poster said, I am honest about a CZ when asked. Generally though, I get "those are pretty earrings," to which I respond "thank you." But if someone asks where I got them or if they're real, I'm honest. And sometimes I have even been known to say that my ering is fake. There are times and places when I don't necessarily want everyone in earshot to see my ring finger as a target.