Not being heartless isn’t exactly mutually exclusive with intent to do bad. Kaido arguably had a soft spot for King. What we know is that Roger and Garp deemed it necessary to team up to stop him. You could also argue that he could be judged based on the company he keeps, which are mostly scoundrels. OTOH I’m pretty sure Whitebeard only sailed with him due to losing the Davy Back fight, and it being dishonorable to back out of a deal.
We know he has no qualms with harming children, and that he would likely do just about anything to accomplish his dreams (like Blackbeard).
This kind of separates them from Luffy, who was willing to forgo his own if it meant helping those who saved him on Amazon Lily. I’ll be interested to see how accepting he is of his own fate on GV.