[MereInterest]

While true, that's a bit of a non sequitur. The value represented by a currency isn't measured in units of that currency, but in terms of what can be bought with that currency. If that purchasing power goes up, then so does the incentive for launching an attack. Therefore, to maintain bitcoin's security, there must be a corresponding increase in mining costs to prevent such an attack from occurring.

Bitcoin requires energy expenditure proportional to the value represented by bitcoin. Anything less, and it is vulnerable to attack. Bitcoin fundamentally does not scale.