And Plato decried the use of writing, for the children would lose their memories.

No he did not. In the dialogue you're thinking of Socrates talks to Phaedrus, and neither of them "decried the use of writing".

Writing had existed for 3 millennia by the time Socrates was alive.

In fact Socrates says in that dialogue:

"Any one may see that there is no disgrace in the mere fact of writing."