To be clear, I don't claim that non-Bitcoin cryptocurrencies do not have value. You're right that their de facto value is revealed through trading activity on exchanges. I view value as subjectively revealed by market prices, not through any sort of labor theory of value or other nonsense.

I'm arguing that non-Bitcoin CCs don't really add any marginal value to the CC ecosystem, and that it's inherently unstable for multiple CCs to coexist. Whatever rationalizations people are making to justify mining Litecoin and holding onto it (ignoring sunk costs of Scrypt ASICs) are inconsistent with reality.