The Harmonium believes that the ultimate goal of the multiverse is universal harmony, and it's ready to spread that belief to all those other sods out on the planes. If it takes thumping heads to spread the truth, well, the Harmonium's ready to thump heads. Sure, there may not be peace right away, but every time the Harmonium gets rid of an enemy, the multiverse is that much closer to the universal harmony it was meant to have. And what happens once the Harmonium succeeds? When everyone is in agreement with the Harmonium, a new golden age will begin. That's why the Harmonium works so hard to get folks to conform - it's all for their own good.
The goal of every enlightened being in the multiverse is to live in perfect harmony with all others. Peace or war - those are the only true states of the multiverse. If a being and its neighbors got the same views, then there's peace between them. When they don't agree, that's what causes war; one body figures it can use fists to convince the other. Now, there's some powers who say otherwise, but the Harmonium believes that peace is a better end than war. For one, all of a body's work won't get destroyed during times of peace. Families don't get killed, kings can actually spend time ruling the people, scholars can study, and petitioners can raise their crops. Everybody, even the fiends on the Lower Planes, can prosper. On the other hand, the Harmonium says there's only one way to have peace: their way. War or peace - squabble among each other or join the Harmonium - those are the only choices.