Speculations The original Twenty Kings were morally gray at worst

[Donquixote Shivercalero]

When they were first introduced chapter 497, Pappag specifically mentions that Modern Celestial Dragons have gotten worse over time implying there was peeps were they weren’t that bad.

Vegapunk mentions that he can’t make any moral judgements regarding Imu because he doesn’t understand enough about him.

Vegapunk mentions that the War of the Void Century was a clash of ideologies and specifically notes once again that he can’t castigate a specific side.

The only deviation from this morally ambiguous framing of th founders of the WG is Tontatta folklore about the Ancient Don Quixotes enslaving them. However even this is not at the same level as Charlos or his family. While yes they did enslave the Tontattas, they also used Tontatta labor to provide for their, human at least, citizens.

 

[Loki D. Terror]

They were manipulated by imu most likely but kings can be greedy and evil anyways.

 

[shastar-sei]

"Power tends to corrupt and absolute power corrupts absolutely."

There's a bad-future concept for characters that Oda sometimes draws in his SBS.

He recently drew a bad-future version of Vivi at age 60, where she seemingly became a Celestial Dragon. Like a typical Celestial Dragon, her appearance took a hit beyond just aging. This heavy decline in appearance is also the case in all of Oda's bad-future drawings. I believe Gloriosa and Miss Buckin are in-story examples of characters who are living their bad futures because of their unreciprocated love for Roger and Newgate, respectively. They contrast with Shakky, who aged gracefully because her love for Rayleigh was returned.

Anyway, most of the First 20's original intent may not have been evil, at least in their own eyes. However, their descendants likely became more Charlos-like over time in both appearance & personality through the continued preservation of their absolute authority. They became increasingly evil due to their reinforced environment, and Oda tends to depict weaker evil characters in an ugly way.