What you seem to be missing is that people don't solely derive value estimates based on the opinions of others. There are business fundamentals which can lead to one or more value estimates under different assumptions. If you don't do your own calculations, you may still read calculations from other people and reach a conclusion as to whether the true value of the stock is higher or lower than the market price.

EMH is about the tendency of the market to be efficient over time. It is purely of academic interest to dream up hypothetical scenarios where everyone is equally rational and informed, etc. There are degrees of efficiency and information, and it's useful to talk about this to try to understand how real markets work and can be made to work better.