Let's take your argument to the extremes of ridiculousness - why has pirate got a scammer tag? After all, it was obvious it was going to go bust. So isn't that a "common mistake" between pirate and his investors - as they all knew (or should have known) that it wasn't going to end well?
Because Pirate committed fraud and his customers did not. Otherwise, you would be absolutely right and the blame, and hence the damages, should split between Pirate and his customers.
In this case, both parties had sufficient knowledge to conclude that Patrick had significant Pirate exposure. And there's no evidence of greater fault on either side.
So what evidence did MP have to draw that conclusion when PH asserted the opposite? What information was there about PH which meant any reasonable person would have concluded he was lieing or mistaken? I was under the impression he had a fairly good reputation - what am I missing? Didn't he do credit-ratings - suggesting he went far beyond normal due-diligence?
Looking back after the facts and concluding "well it should have been obvious..." isn't much evidence of anything. Is it really your assertion that ANY investment paying 1% per week (or whatever he was offering) back then MUST have been invested in pirate? Was there NO alternative? Was PH's reputation SO bad that he deserved NO credit for doing due diligence?
If you're going to assert that something was common knowledge (in this case that it was common knowledge that PH was invested directly or indirectly in pirate) then:
1. You should prove it.
2. How come PH didn't know? If he didn't know how can you reasonably assume MP must have? Or are you saying he DID know?
You see, point 2 is the key one. PH had MORE information than MP (deposit details). If PH couldn't draw that conclusion it logically can't make sense to assert that someone in MP's position MUST have known it. The alternate, that PH DID know (and MP should have) would be an automatic scammer tag - as then PH would have misrepresented himself when making the contract. You can't have it both ways - that PH didn't know but MP must have known. So which is it?