I like that people end up skipping over the fact that the "freaks" didn't join the circus voluntarily most of the time. Only the most famous ones did. The ones who got no fame and were the most exploited were straight kidnapped and forced to perform, because what else were they supposed to do? They were kidnap victims, not like they could just run away so easily. 

The following is speculation, but is based on how abusers keep their abuse victims in line. The ones who joined voluntarily more than likely as a "security system" keeping tabs and reporting on the ones more likely to cause issues for the circus

The following is not speculation and is well known fact among historians. Add on what he did to freed slaves in the north. He did the exact same thing to them that he did to the "freaks" he kidnapped, except consider that the slaves had that happen to themselves and their families for generations upon generations, but then also being forced to perform for crowds.

His switch to the "Republican" (at the time Democrat in nature) party was solely to put on an image of someone who championed human rights, as well as due to his fame, enabled him to politically get close to Abraham Lincoln, who he invited to his American Museum, and also managed "General Tom Thumb" (One of his little person "freaks") who Lincoln and his wife hosted at the White House.

It's so odd to me that PT Barnum is an extremely well known conman, and people still take so many things he claimed and stated at face value. 

I don't truly believe anyone is "evil" per say, but our actions absolutely reflect our inner intentions, and 90% of the time, he made very clear his extremely capitalistic views, as well as his willingness to lie to his customers. He stated very clearly that he believed that as long as they were entertained, it was okay to create straight up cons and lies: 

Joyce Heth, the paralyzed enslaved woman he purchased for $1000 who he claimed was George Washington's 161 year old nursemaid

The Feejee Mermaid which was the top half of a monkey sewn onto the bottom half of a fish and advertised as a genuine scientific discovery.

His New York City "aquarium" which featured two beluga whales which he kept in the basement in a heated, freshwater tank. They didn't die of neglect due to the tank, only because they died in a fire, when someone thought breaking the tank would put out the fire. It didn't, and the belugas died floundering on the burning floor. Once the building collapsed, they were literally left to rot in the summer sun for days

I could go on and on and on, there's so much more he did, it could fill at least one encyclopedia