You're defining the problem away (No True Scotsman fallacy). Instead of deleting articles that are not-notable (according to criteria X) you suggest deleting articles that are spam (according to criteria X). In both cases, you'll need some sort of mechanism for performing and reviewing deletions. Many of the articles in AfD are, in fact, spam.

So, the gain of deleting articles seems to be clear to you (you are in favor of deleting spam), it's only the criteria which lead to deletion that are up for debate.

Deletion of something may be worth re-examination/arbitration because both "sides" of the argument may try to game the system, particularly if a negative vote on AfD was eternally valid. Banning further discussion and modification also seems contrary to the wiki spirit.