To say it's drivel and that Plato was being inventive, as if it were a matter of fact, is really not being any more helpful than categroically saying it was definitely at a given location and that he was writing from direct experience. Thera as a source for his imagination or even as a location for his experience or knowledge have been voiced but no answer as yet has anything except cicumstantial evidence. "There was never a land mass out there in the Atlantic" - says who? because we have no evidence for something doesnt mean it wasn't manifest. You could of course be right, but so many archeological locations have been categorically attributed to legend legend prior to the answers coming to light. Troy jumps to mind. As for the place, for argument sake lets say it did exist, I am not sure that that even had he definitely meant it being "out there in the Atalantic" it would neccessarily mirror our current vision of what "being out there in the Atlantic" means. Perhaps Plato knew it to be beyond The Pillars of Hercules but in that he failed to be precise, why not inland from the present coast-line?