I would understand Dumbledore confiscating the map. But, if he were to confiscate it, he would do only that, not Obliviate the Weasleys such that they’d have no memory of ever possessing such a map. It would seem cruel and pointless to him.
Suppose Dumbledore thinks his enemies aren’t aware that the map exists. If he believes one of his enemies is a Legilimens and is periodically scanning the students’ minds, he might not want to take the risk of them scanning the Weasley twins and discovering the existence of the map. But I admit I’m stretching at this point.
I would understand Dumbledore confiscating the map. But, if he were to confiscate it, he would do only that, not Obliviate the Weasleys such that they’d have no memory of ever possessing such a map. It would seem cruel and pointless to him.
Suppose Dumbledore thinks his enemies aren’t aware that the map exists. If he believes one of his enemies is a Legilimens and is periodically scanning the students’ minds, he might not want to take the risk of them scanning the Weasley twins and discovering the existence of the map. But I admit I’m stretching at this point.
If that enemy exists, he already knows.
Upvoted for qualifying the clever argument with the admission that it is a stretch.