Daniel Siegel talks about 'coherent narratives'. Didn't matter what kind of insecure attachment people had with their parents (ambivalent, avoidant, disorganized), those who developed a coherent narrative about their childhoods were able to parent their children well and create secure attachments. If you zap away those memories, then how can you achieve a coherent narrative? Maybe a blank slate is good, but I would imagine turning over those memories until they become a smooth stone and not a shard of glass would make you a richer, wiser person.
Maybe this therapy is better for war veterans, for example. Hard for me to judge since I've never had recurring nightmares and intrusive thoughts as a result of that kind of trauma. However, seeing the effects of EMDR, that might still be a better way to go than 'zapping'.