I was actually watching the original film the other night, and I was thinking that while it does a decent job of pointing out the hideous nature of the circus, a longer, slightly more mature, but potentially still child-friendly, film could make a better argument for this. Especially if it focuses on the mistreatment of animals by circus people.
However, I don't think this film will be interested in that, since a message like that would take away from the forced whimsy and tiresome gross-out jokes Disney has in store instead. And I guarantee that there will be at least one adult male in this version, since Dumbo's too small and cute to make a big pile of dung, and as Hollywood has taught his, females don't poop.