Amanda told him to let Johnny know Robby was with them. He was Robby's father, he had the right to know where his son was.

Intellectually, Daniel agreed.

But as soon as he saw Kreese standing next to Johnny, it gave him all the excuse he needed.

He'd make a better father-figure for Robby than Johnny ever could. Would Robby really be safe with Johnny if he'd allow scum like Kreese to hang around?

Daniel had to look out for Robby's interests.

And what of the kids in Cobra Kai? Shouldn't their parents know about Kreese?

They weren't his problem.