Anarchism isn’t non-violent. To assume anti-oppression and pacifism are one and the same is to make the same mistake Engels makes in On Authority.
Authority is violent, but violence is not authority.
Edit: on this topic I’d recommend Anark’s video on Power, where he explains that anarchism seeks to create a horizontal power structure. It is not the absence of power structures, it displaces oppressive power structures with egalitarian ones.
That’s actually kind of genius. It’s even made of lead!