I believe that in most cases non defensible wars are morally wrong, but sometimes it is necessary. For example, if the Allied powers had stepped in and stopped hitler in the early 1930s when he was railing against the allies and jews, WWII would have been delayed (although it probably still would have occurred eventually), and the holocaust would not have occurred. A preemptive strike would have saved the life of millions of Jews
Technically, at least. Whether or not it is smart or wise is another matter entirely. Societies can manage to justify practically anything to themselves. Take America, for example; our ancestors were able to justify the Native American gennocide and Japanese-American internment based on their values and judgment at the time. Religion is also a very effective tool in justifying what most people would view as atrocities.
While a large number of non defensive wars have been for ideological or religious reasons and therefore unjustifiable, there are also non-defensive wars which are justifiable. Some may be in responce to threats from a neighboring country, or because the other nation is committing some sort of genocide. In these situations a non-defensive war may be justifiable.
In theory, the only just reason for militarization is to defend the nation, against actual threats. The only other reasons are for conquest or draconianism. Like just cause you dont like another nations culture does not give you the right to fight against it. Every other war since WWII has been a blatant blunder, because none have been about defense, and just pointless violence.
After WW2, the US imposed a pacifist constitution on Japan - and they love it. We need to have a pacifist constitution ourselves, otherwise we are hypocrites. Further, only Congress has the power to declare war, but conflicts are okay by the president unilaterally declaring, provided it follows the War Powers Act. Congress needs to get rid of this law and face the consequences of declaring war (and conflict). I remember US legislators urging the President to act in Syria, while he wanted Congress to vote on it - that's the way its supposed to be. Commander in chief (CINC) means he commands the troops, not declaring war. I think the founders intended CINC to lead the charge as did George Washington...
Every government has its own allotted land. Each government gets to govern what happens inside that land, and should use only economic influences to affect what happens outside of that land. Not all governments will follow that moral code, so all governments have the right to a military for defense purposes, but those militaries should be used only for defense purposes. Attackers and aggressors shouldn't be viewed as heros.