Well, of course war propaganda is offensive. It's not meant to be taken as kind and enlightening. Depending on how it's used, it's supposed to either rile up the people of a nation against a common enemy. Or, if used by your enemy, to demoralize the people of your nation. You don't get a reaction either way by being polite.
Yes, war propaganda is offensive, because a government should not be manipulating its people into wanting to go to war. People should be able to choose for themselves whether the war is appropriate, based on accurate information. People should never be taught to hate people of another nation or ethnicity, because that is not helpful or healing.
War propaganda is designed to be offensive by its very nature. It's designed to disturb people and get them on the side of their home country. Therefore, such propaganda is offensive by design and that won't change anytime soon. Some countries take the offensiveness to another level, though, in order to shock people.
War propaganda is necessary during times of war. In face, the use of propaganda is a humane form of conflict since it does not use physical violence. If a war could be won by only using words, it would be preferable to a conflict that kills and injures people and destroys infrastructure.
Is offensive used here in terms of offending someone, or in terms of an offensive - ie: an aggressive act. Propaganda is part of war, and is considered part of the war process. Propaganda during an ongoing smaller war is also part of the war, but it is equally important - in this case, to set the narrative.