First, breaking a law isn't by itself unethical. You can argue otherwise if you like, but a) it opens up a whole slew of absurdities (e.g. exploiting a software bug on a slot machine for profit is unethical IFF it's on a network that crosses a state line - https://en.wikipedia.org/wiki/United_States_v._Kane), and b) you'd be abandoning everything you've said up til this point.
Second, copyright law is not a rule that is "attached to every sale," whatever that means. (If it were, you could get around it by shoplifting!) You need to stop blurring the lines between legal rules and ethical rules, because it's led you to confuse the difference between agreeing to a rule and being subject to it. So, let's make that explicit. I'm subject to copyright law. Doesn't matter if I agree to it or consent to it (it's not even clear what consenting to a law means), I'm subject to it regardless.
Now, you can certainly argue that there are ethical laws that we are all subject to as well. But, you are not arguing that! (correct me if I'm wrong, of course) You are arguing that there is an ethical law against piracy that pirates have agreed to, without wanting to, and I'm telling you, that's not a thing that can happen. You can't agree to something against your will.
So, you gotta make a choice to make this whole line of reasoning coherent. This ethical agreement not to pirate stuff, is this something that pirates can refuse? If so, I think they very clearly are refusing it, and if not, you cannot meaningfully claim that they agreed to it.