Pause.
They think they could pretty finely affect his powers - moreso than we could, actually, we were braced to survive and fix a black hole but we didn't actually have a way to prevent one - and without understanding how you could work for Melkor without sharing goals with him, they would probably have made his magic stop working and held him in Lórien while they tried to understand what all this meant. Oh, and offered to let him go if he agreed to them changing his mind so he thought it'd been a wrong thing to do, we're explaining to them why that's a bad idea. And they'd have put the other Valinor back - they might have needed to rescue and consult their local alts first, they really really don't understand any physics - and their first thought would be to interdict summoning again, but as soon as someone pointed out mortals needed it, they agreed that making daeva powerless near Valinor was a less intrusive way of achieving what they wanted, I think they would have landed on that even without understanding things better.
And then they'd have spent Years trying to figure out what to do because of not understanding urgency. And given Cam the run of Valinor once he seemed to be visibly suffering from containment to Lórien, they think - they're confused about what demons need and so are we -