I'd like to ask myself the opposite, when is it unethical to pirate? Because it's just data, and how many copies there are of it shouldn't change anything. If I want to support a developer I'd 'buy the product', regardless of already having it or not, and I would never in my life buy a product (Not a service, just the data) just because I cannot get it otherwise. I believe it's pretty much the same for most people that knows how to download pirated content.

But I believe that early leaks are strongly unethical, as you end up interfering in the creative and production process before it's ready. Furthermore, a lot of people whom usually won't pirate will jump at the possibility of doing so just for the hype of getting the product NOW, and maybe will not feel the necessity of buying later. I cannot think any case in which a leak is ethical or even beneficial for anyone, and I'm surprised that I've never seen much push against it by pirates.