One interesting theme of the Beast Pirates is how Kaido "dehumanizes" his subordinates and turns them into animals. You can think of Kaido, king of the beasts, as a beast tamer. The all-mighty mythical eastern dragon is the god of all animals and rest of the animal kingdom is at his beck and call. One reason why I believe Oda made Kaido the only mythical Zoan in the Beast Pirates (Orochi is doing his own thing with his own subordinates over in Wano, but they still very clearly serve Kaido) was to visually establish the hierarchy between Kaido and the lesser animals. The calamities, the Numbers, the Flying Six, all Zoan-themed but lesser Ancient Zoans and below. All the way down to the Artificial Zoan, those flawed partial animal SMILES, and regular riff raff like the Waiters who are in line to become some inferior form of animal themselves.
Expanding on the theme is how you see typical behavior in the Beast Pirates has been influenced by Kaido's philosophy that they're all animals. Jack introduced us to the Beast Pirates. Jack is a simple brute, a barbarian, he wants to wipe out Zou and he won't take no for an answer. Limited intellectual or emotional capacity, he's not there to reason. He's what you call a complete animal, no offense to the actual animals who live in Zou of course. The Minks acting like civilized saints was dramatic irony. Jack brought with him the Gifters and the Pleasures, one which have been partially transformed into beasts and the other have become less human by virtue of their lack of emotional expression. What kind of human can't even cry? The Pleasures laugh at their own pain and their own defeat, they been dehumanized inside Kaido's crew.
Another interesting phenomenon is how people in Wano not part of the Beast Pirates have been influenced by this theme as well. We have Urashima, a local Yokozuna of Wano who has never been a pirate a day in his life, eating dinner with Mouseman who whispers into his ear how he should live his life. Mouseman tells Urashima that if he wants Kiku, he just take her by force. They finish their serving and Urashima tells the shop owner he wants to eat his prized pet, and that he can't be refused. Urashima was not being enabled his natural inclinations, he was being transformed into an animal by the influence of the Beast Pirates.
Finally, in Udon prison we get a look at just how exactly Kaido conducts his recruiting policy, what he thinks it means to be a member of his crew. He wants to break Kid, Luffy, and Kamawatsu's spirits in prison. They have good potential, but they will run around like Shutenmaru and never serve him otherwise. Kaido needs to put them down, he has to subjugate these people before he believes they're ready to be Beast Pirates. Normal people may join pirate crews because they're inspired, they were convinced, they were recruited through some sort of connection. But words and emotions aren't how you train or domesticate animals. Kaido himself directly breaks people with force in order to turn them into simply beasts that obey, fear him and engage in endless fighting. In essence, the Beast Pirates are truly a crew of non-humans.