'Orthaic, let's say the value did drop by half: why would it make a difference if you had mined them.'
Because you didn't invest money in them, you invested time. The time stays the same, what you can get out of that invested time doesn't.
The difference is psychological, you can never recover the time you have invested. You can recover the money (or part thereof)
Imagine that you are going to a concert, and you paid €40 for a ticket - on the way you lose your ticket, you're really annoyed because you can't get in now, you've lost €40 worth of value PLUS your time which you can't get back.
Yet on the other hand, on the way to the concert you lose €40, you continue and use your concert ticket to enjoy your evening. Still annoyed that you lost money... You don't lose the time. (most people would not buy a second ticket, perhaps because it feels kinda shitty to pay a second time for something when you've already paid the first time... )
I don't know if i'm explaining the psychology very well, but there is a difference.
'Time has its monetary value. Time spend on mining Bitcoins has its opportunity cost. There is no difference between spending money outright by buying Bitcoin and foregoing profitable opportunities because of mining it.'
There is a huge difference, because how we value our time and how we value our money has a big psychological impact on what we think of as a loss. Today my bitcoins are worth $10,000; so i'm $10,000 better off than when i started investing time in the mining of bitcoins.
If i i started out with $20,000 and bought bitcoins, which are now worth $10,000 then i've lost $10,000.
Very different from a mental point of view.
"Time has its monetary value." - Yes, but you have to do the conversion in your head, a mental operation which is more flexible than $20,000 > $10,000 (no conversion because you are measuring both in the same units.)
There are some very interesting studies on behavioural economics, and cognitive science (how we think about things) and cognitive illusions - which illustrate the false thoughts we get when equating complex things, and the decisions we make which are not strictly rational (as an economist would like to assume)
@Maniac: I think you've hit the nail on the head there:
"The value of any currency can only be judged relative to other currencies (and possibly gold and major commodities)"
The value of a currency relative to currency markets, and the purchasing power are two DIFFERENT values. The number of cupcakes and the number of dollars i can buy with my Euro (or Bitcoin) may vary separately. (oh, goldfinger already said this, sorry)
"You need someone in control to tinker with the tools in those situations, which is why I said Bitcoin needed regulation" - and that may be true, but bitcoin has an algorithm, which offers stability, and thus confidence. Regulation and tinkering with the supply (which is what eve economists may do when there is a PLEX price bubble) are two separate ideas. Regulation is about the law, bulk transfers, taxation, capital flight. And bitcoin has virtually none (probably something governments do). Controlling supply/inflation is something Central banks do. (and Bitcoin has a algorithm)