> 1. Basically anything that's expensive has had its price inflated in some way. That doesn't make it anyone any less willing to pay the price.
That doesn't make sense. Liquid expensive things like gold have a market price plus some transaction fee or fee for storing etc. Even illiquid expensive things like houses cost market prices + transaction fees + fees for agents etc. The point here is that diamonds are marketed like liquid assets when in fact they aren't.
> 2. Same as number 1. Lots of things are only expensive because they've been marketed well. Does that make them less valuable?
Yes, unless you define value to be 100% subjective, in which case, no.
> 3. No one buys an engagement ring as an investment. Who buys an engagement ring thinking they'll be able to recuperate costs?
I've had lengthy arguments with family about this. Engagement rings aren't bought as an investment but every single person had the expectation that diamonds are an investment, and as such can be resold, will appreciate (at least not depreciate) etc.
There are valid reasons to buy a diamond, don't get me wrong, but the large majority is not aware that diamond rings loose 30-50% of monetary value the instant they are bought.