That's entirely possible, and very likely. However, that does not do away with rationality completely. For some given situations, with data on the situation and a set of options, we can deduce pretty quickly what is rational to do, what is right to do, and what is in one's interest to do. This is how we (and that includes me and you) are able to criticize people on those grounds all the time. If someone is poor and has a choice between buying a stereo system and saving the money in a high-interest bank account, I doubt you'd have any problem saying that it's in their self interest to do one of those options and not the other. Economists talk about the principles of economic rationality all the time.

So yeah, you can have your own opinion. That doesn't mean that the opinion is beyond criticism, nor does it mean it's a rational thought out opinion from all points of view, considering all the facts.