All it says is that there was never any reason in the first place to suppose there's a difference between possibility and existence.

That's good to know. So the next time someone tells me that something might be a cure for cancer, I won't have to think about it or research it, because if it is possibly a cure for cancer, then it is actually a cure for cancer. And the next possible theory of 9/11 that I hear, I don't need to wonder if it's true, because, being a possibility, it's also an actuality. And I don't need to worry about what you actually mean by your writing, because whatever possible interpretation I come up with, that must be the actual intended meaning...

Wait - you're saying that's not what you meant... that all those possibilities which seem to simply not exist... you're saying that they do exist, but somewhere else, in some other world? Well, uh, that's an interesting idea... pretty radical... I don't see what evidence you could have for it... but I guess I have to admit it's possible, ha ha... But wait - isn't it also possible that these other worlds don't exist? So does that possibility - meta-possibility - "exist" somewhere too?

Now please note: I am not disputing your right to build byzantine multiverse theories and to engage in abstruse logic-chopping which will allow your new interpretation of the word "possibility" to become consistent. But it is absurd to say that "there was never any reason in the first place to suppose there's a difference between possibility and existence". You may as well say there was never any reason to suppose that the Flying Spaghetti Monster doesn't exist, or that there was never any reason to suppose that black isn't secretly white as well. There are clear differences between the everyday original meanings of possible and actual, and proposing to negate them by supposing that all possible worlds are actual is radical metaphysical innovation, and before I believe it, it is reasonable to request some evidence, or at least an argument in its favor.