Irrational is not the same as stupid. The irrational - often disastrous - behaviour of heads of state when they launch hostilities against another nation is not necessarily the result of stupidity, but of fear, hunger, hate, self-defence, power-lust, desperation, ideology, greed, influential interests within the country, coercion from a more powerful ally, or some complex of political, economic and sociological factors.
Stupidity and ignorance are also different: a head of state who starts a war may miscalculate his chances of winning because he can't do the math, or doesn't know the enemy - or he may base a rational decision on incorrect information from sources he trusts.
Roughly the same rule applies to individual choices.
An error of judgment is not immoral: it's intent that makes an act morally right or wrong; outcome that makes it strategically right or wrong.
(The irrational behaviour of the species as a whole throughout its history is the result of too much intelligence, not too little. Big brains are more prone to insanity than little ones, just as complex machines break down more often than simple ones.)