The perpetual motion machines are indeed a bad metaphor.
But the question which fork will prevail a valid one. If you had stake in ETH and ETC, why would abandon one over the other? How many forks till trust evaporates?
Hmm, I'm not sure there is a limit. I mean, if each fork gathers a significant fraction of support for a long period of time, it would reduce the effectiveness of every related chain. But that's unlikely I think. There tends to be one (or maybe two) chains that get the vast majority of support. So I'm not sure forks like that are that much of a concern. What's more of a concern would be if the majority follow a chain that has unfixable design issues.
But the question which fork will prevail a valid one. If you had stake in ETH and ETC, why would abandon one over the other? How many forks till trust evaporates?