To me, a good litmus test to see how fucked up someone is, is how they treat those close to themselves. Cause if BM is willing to treat her own children like tools, has zero sympathy or respect for them, then that clearly means she sees those civilians as even less than that.
Not always, big mom has her moments when children or food are involved, she tried to protect otama and she got mad about october town getting destroyed after those people were kind and gave her food.
Kaido doesn't give a shit about anyone unless they're strong. Even then he only wants to use them for his own reasons, he would have rather killed Yamato than let her leave on her own.
Big mom will use her influence to "protect" a territory to an extent, if they provide her with food she likes and those people are at least able to maintain somewhat normal lives.
Kaido on the other hand, enslaved an entire country and works their citizens to death to make weapons that he either uses on other civilians (or pirates or marines). The country he took over was dying, the people unable to feed themselves and without so much as clean water.
Kaido is a way bigger asshole, way easier to hate as a villain. Big mom is also pretty bad for sure, but honestly the worst part about big mom is her design