It's moisture content is certainly a problem, but that's up to the pizza maker to counter. A good pizza maker should be able to deal with it, either by separating it from the base better, removing excess liquid first, or adding the pineapple later in the cooking process even.

I agree that it doesn't pair well with those cheeses, which is why I use a cheese that matches better with the pineapple when I'm using it. Having a Chedder or similar, and then maybe some parmesan gives the salt content, the cheese content, but doesn't have the problems of the cheese flavour being overpowered by the pineapple. Also, if the pineapple is the dominant flavour, you might be using too much of it.

As for point 4, many ingredients are difficult to grow in some areas, and expensive. I don't see why that should exclude them from being on a pizza. It's a cheaper ingredient than say, pulled pork, which seems to be quite a popular topping currently. And certainly cheaper than king prawns and I'm not sure where pizza would be without prawns. Not that it's a common regular topping, but I've had truffle on pizza also, and saffron used for flavouring some things on it. Pizzas aren't just cheap food anymore.

Sure, i'm pro-pineapple. But like most things it doesn't belong on every pizza, just like anchovies or olives don't.