Kid Loki, who was 20ish btw, challenged an adult and wanted to participate in adult businesses. He got the adult treatment. Xebec didn't humiliate Loki, he honored him.
Teach would do anything to achieve his goals. Which is fine, he's a pirate for gods sake.
Besides, Luffy didn't hesitate to join forces with Croc, Bege or Kid. All shady, all confirmed murderers, all mobsters and women abusers.
Which is also fine as Luffy is a pirate too.
Xebec and Teach at least aren't hypocrites. Luffy is the worst of them all.