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.