You're underestimating the power of speculation and greed. You scenario will never happen as long as human nature doesn't change. If too many people move to on

You're underestimating the power of speculation and greed. You scenario will never happen as long as human nature doesn't change. If too many people move to one chain, the speculative expected outcome of the other chain will rise, leading some people to switch back, etc. This is the very reason why Bitcoin works.