Oh this is delicious. Why should Macbeth believe Goliath here? We don't know Macbeth's story yet, so we could just think here that he doesn't know Demona that well! But the truth is that there is perhaps few who could ever know Demona so well as Macbeth.
If these gargoyles had been just any gargoyles, ones Demona didn't know that he'd gotten his hands on, I do think she would in fact come for them. She doesn't want to be alone; she does want a clan of her own. And after such treatment at the hands of a human? How ready might they be to follow her path and not a path like Goliath's?
But the anguish on Goliath's face? I'm going with that's what convinces him. Anyone might make a lie, saying what Goliath does, to spite their captor, undermine them. He could assume it's a lie. But again, he does actually know Demona, and I think maybe he recognizes a bit of what is going on with Goliath here. In the face of that agony and the reality that these gargoyles also do know Demona not just as a leader or another gargoyle, but personally, he believes it. But also... it's a kids show and there's only so much time left in the episode. Much easier if he believes it for that reason. But still, going to attribute everything I can get away with to in-universe reasons, and I think it's a fair reading.









