Now in the unlikely future event of a real schism with two persistent forks, it doesn't affect current investors. They can sit tight and whatever happens their money is safe. For new investors of course they have to make a choice (or hedge between them), but that is natural given there was a real schism in the economic majority, which suggests there were good reasons for it. I don't think hardly anyone is going to invest in a smallblock fork versus a reasonably larger block fork, for example. If we assume a major schism where investors support both, which seems very unlikely, then there was probably a good reason for it.
This is my argument about say increasing the block size. There seems to be deep division about whether this is a good idea or at least whether some of the specific proposals of how to do it are a good idea.
Maybe you are right and trading would resolve the issue quickly if people had to put their money where their mouth is rather than just make a lot of noise over it. But if not, then exchanges, wallets, payment processors, etc. could be set up to deal in hedged baskets which consist of one of each coin traded together. Those who did not want to bet on one or the other could just use the basket until the market sorted out the question one way or another.
In no way is this a suggestion to simply let the chain fork as much and as often as anyone wants without the necessary infrastructure in place at both the exchange and wallet level to deal with it in a non-disruptive manner.