Why are you so consistently trying to distort the meaning of the words?
If someone gave me 100 bitcoins and I lost them, that would mean exactly that, i.e. losing 100 bitcoins, and I would say that I lost 100 bitcoins, as simple as that. But that doesn't in the least mean but they cost me anything in monetary terms (let's assume for simplicity that I just found them to avoid unnecessary complications). Loss and cost are different things, which you seem to be deliberately trying to confuse here, again. Aside from that, costs have nothing to do with either realized or unrealized gains. Open any economic dictionary (or textbook, for that matter) finally and read for yourself. Gain (otherwise known as profit) is the difference between what you received when you sold the coins and what it cost you to obtain them. If this difference is negative it will be a loss. I'm really fascinated that you are still trying to continue this futile argument, or do you really think that having the last word in it will somehow make your point more plausible?
You can keep the last word. Seems pretty straightforward to me where the incentives lie. It can cost 0 Dollars to lose 21 B. So it costs nothing. Seems legit.
Indeed, it could cost nothing
If you didn't spend anything to obtain 21 billion dollars' worth of coins, your costs would be effectively equal to 0, so it is perfectly legit. Imagine that someone has sent you 50% plus 1 coin to your wallet, and now you can either destroy the coin or sell the coins. Destroying the coin would mean that you lose a certain amount of some other currency which you could receive if you chose to sell your stash for that currency. But your costs associated with the acquisition of this stash will be the same in either of these cases (read you could destroy the coin in question without spending anything). I guess that should help somehow at last
I already understood your point, as I am sure you understood mine.
I do not think acquisition costs are the only costs towards incentive to attack or not attack.
In the very least, you are massively misusing or rather confusing the terminology here
And to tell the truth, I don't understand what you refer to here by using the term "cost". Honestly, I'm heavily inclined to think that you don't quite understand yourself what your point is. If you don't talk about costs (expenditures or expenses) involved with buying 50% plus 1 coin of monetary supply (as you said yourself), the closest approximation to what you might mean is opportunity cost, i.e. the cost of choosing a less economically favorable option before a more profitable one. Obviously, the latter would be equal to selling the coins at the market price, but as you have also been told already, you won't be able to sell at exactly that price and, apart from that, you explicitly discarded that option yourself (probably erroneously). So it kinda looks you don't know what you are talking about