What might appear to be irrational behavior to you is just due to people making decisions based on different information, differing priorities and a different decision making process informed by different life experience. If someone's decisions appear irrational to you, you just don't possess enough data about the information they have access to, their priorities and the world model in their head.
So basically what you're saying is the word "irrational" has no meaning whatsoever, and that every act is rational, just perhaps not to your point of view or level of information.
In the theoretical sense, I agree with that, but in a world of social interconnections, we need a meaningful framework and vocabulary for judging these sorts of things. While I believe that true objectivity is hard (and maybe impossible), I think there's a lot of social value in coming up with widely accepted definitions of rational vs. irrational, at least on a case-by-case basis.
I think you are mixing up "rational" and "reasonable". It is not rational to flinch away from that puff of air you get at the optometrist, but it is reasonable.
Why is the assumption "governments are rational" more reasonable than "governments are irrational"? Both seem equally possible to me, given the fact that we don't have the information to tell, either way.
In any case, that's a false dichotomy. Governments are not uniform entities, and there's no point talking about them as if they are. Governments, like people, do some rational and some irrational things.
Because it takes quite a lot of work and training for individual humans to act rational. Therefore, without other information, it is a better default assumption that any given human or system-of-humans is non-rational.
