According to Osho, he doesn't call husbands donkeys; he was voicing the wives' ironic viewpoint. His deeper point is that the roles of husband and wife are social fictions that turn living love into ownership and duty, breeding quarrels and hypocrisy. Honor love itself - free, respectful, and mutual - instead of clinging to institutional labels that make persons into property.
He doesn’t think husbands are donkeys; he’s saying labels like husband and wife can make people bossy and fake, and love works better when you treat each other kindly without trying to own one another.