[makomk]

In particular, perfect information is required in order for the free market to allocate resources efficiently; if obtaining information has a cost, there are all sorts of fun ways to abuse that in order to break competition and misallocate resources. You can see this in the US cellphone industry - by increasing the complexity of their plans, cellphone providers have made it more expensive to comparison shop, meaning that customers (rationally) go with the first option rather than the lowest-cost one.

You can also see this with some of the smaller-scale Ponzis and investment scams - so long as the amount of money each investor has invested is much smaller than the amount it'd cost to investigate the investment, it's not rational for them to do so. One of the recent US Ponzis, Perma-Pave, actually failed because they got greedy and took on a large investor with reason to investigate what had happened to their money.