All valid points. But Mr Walker was still in Command and had the opportunity to say no. He succumbed to peer pressure from more experienced people.
Their actions in encouraging him were wrong and there are moral issues around it. But the PIC could have just said no. At 120hrs he should have known the rules and abided by them. The PIC could have quite easily flown 3 circuits before departure and the flight would have been legal. As a licensed pilot he knew the requirements and should have insisted that he did this. He could have done these with the CFI who was onboard for the outbound leg. That covers the legality of the flight.
The next is the poor decision making displayed by the crew, they did not lift enough fuel and they did not divert, that was poor planning and poor command decision. They did not die on the outbound flight they died on the return. They could have diverted at any time, why did they not do so? Was the CFI involved in that decision making process? Hardly when he was not on board. The crew choose to push on and it cost them their lives.
The CFI's should not have encouraged him to bend the rules, that was just stupid, but what was more stupid was the subsequent poor decision making.