"It doesn't have to say that. The state is only entitled to collect taxes and fees, that's why the requirement only applies to that."
I rather think it DOES have to say that. There is nothing in it anywhere to even hint that it is limited to state monies only. It says "tender in payment of debts". It does not say "tender in payment of State debts", or "tender in payment of debts to the State". Considering the complete absence of any indication they meant something else, I suggest the words be taken at face value. And if it does not apply to individuals, why does part of that same sentence say "or law impairing the obligation of contracts"??? Are you going to say that part applies only to contracts with the State? I don't think so.
"However recognition of the state is not required for any other financial activity, in any currency. If you want to buy a widget from me for Euros, or Yens, I will sell it to you. Not illegal. You can even send me those Yens from Japan, and I will receive them through an appropriate, registered and licensed financial services company (PayPal, or just my bank.)"
Yes and no. I retract the bit about "requiring" that it go through an exchange first. But that's actually completely irrelevant. I could pay you in buckets of piss, and if you accept them, fine with me. But a State cannot "make" buckets of piss legal tender. That is the point being discussed here.
The second thing I have to say about that is no, you can't do that through PayPal. I know, because I've done it. You can accept foreign currency into your PayPal account, and you can pay in foreign currency from your PayPal account. But nobody in the U.S. can require you to pay a debt in foreign currency, PayPal or not. Again, that's the point here. And if you are required to pay a debt in local currency, sorry, but you CANNOT pay it directly with Yen in your PayPal account. PayPal will first convert it to dollars (and charge a fee for that conversion), before paying in dollars. I have bitched about that requirement more than once, but that's the way it works. Look it up.
"Businesses do receive foreign payments into USD accounts,"
Businesses receive payments in dollars into USD accounts. But if it's a BANK account, and it's foreign currency, it is converted to dollars before going into that account. In many but not all circumstances they will also charge a small fee for doing that conversion. Banks that do not routinely do Forex (foreign exchange) do not do it for free.
"I can receive payments in CDN, and if they land into the CDN account they won't get converted into anything."
That's true, as as I already stated, that's true of PayPal as well. But it's also completely beside the point. If you want to pay somebody in dollars with it, it is still first converted to USD. And often there is a fee for the service.