I understand and you are right, the big ocean is so full of mystery...we are yet to know half of lives down there. The earth is 70% water, even mysterious land animals are yet to be uncovered and to speak about what's in the water....
But the arguments against the survival of Megalodon is that like the Great White, Megalodon was a warm water predator cruising at the coastal, but not such deep water predator as the temperature can be so low ( but then what about the water being extremely hot deep down there with the presence of valcanos? Around this temperature, it should keep the water warm enough for fish that requires it )...besides it must be with such high metabolism, and they definitely can't be feeding off squids, what would those dagger like teeth be designed for if not to take lots of big fish besides squids ( if Megalodon did at all ).
And being so big, it should be spotted...and there should be more than one, breeding...and the numbers should be increasing if it's surviving. Who knows...so they speak until they got shut up like they did with the survival of Coelacanth, Megamouth Shark, Giant Squids and so on.
I am not on any side of the debate, but to think of a Meg surviving in the deep ocean still sounds very exciting as well as shocking..it's a pretty scary stuff....if they have survived, maybe they have evolved...that they went deep under the sea and come out rarely...that would suck if such thing Meg does, I would prefer Megs coming and attacking like Great Whites.
The best is not not expect so much from Megalodon...it can be disappointing no matter how magnificent this predator truly is. Can a Carcharodon Megalodon ever disappoint? How big was it truly? The first eyewitness account was truly unbelievable...