This term is among a cadre of other words that are increasingly applied to positions or parties or principles or people that we disagree with profoundly. Rather than engaging claims we are opposed to and grappling with a competing rationale or worldview, this label of ‘irrational’ allows us to walk away from the conversation. Indeed, once applied, that position or person has been labeled as, essentially crazy - and ‘without reason.’ Why then would anyone - yourself included - waste time considering it?  

From one perspective, it is both unfair and dangerous to use the terms "irrational" to refer to views we find wrong, inaccurate, and/or dangerous (unless of course they are ALSO irrational). That is, if we expand the meaning of "irrational" too broadly, then the word will still have its other meaning (irrational as crazy, inherently contradictory rather than just untrue, and with no sensible means-end thinking involved). And the result of that is likely to be an expansion of mere name-calling.