I was thinking about Goldoa's 'no interference' policy when I came to the conclusion that the Serenes Massacre was probably directly related to the circumstances surrounding Lehran and Altina's child. Usually when I consider the laguz-beorc prejudice or the history leading to that event, I'm putting it in a character's voice, and am left with one thought:
Damn it, Dheginsea, shove your ideals where they belong and commit to something.
From everything I've seen in PoR and RD, Goldoa is the only laguz nation everybody cares about. They have influence. The laguz rulers will answer Dheginsea's call for a meeting even if they're basically at war with each other, a Goldoan dragon seems to carry significant weight even with the Daein military, that sort of thing. Even Begnion probably can't completely ignore them. This is a product of their massive destructive power, of course - I doubt it has anything to do with respect on the part of the human nations.
Radiant Dawn sets Dheginsea up as the ultimate reason why Ashera had to be awakened. He remained stubbornly neutral even when his own children left and got involved in the wars of other nations, he confined his protests against laguz slavery etc. to formal protests with the Begnion government, and all he ever seemed to say to the laguz tribes was "don't make war." His inactivity definitely contributed to the problem. I won't deny that. It's frustrating to follow the story and realize... if he'd stepped in and helped his daughter, for example, Rajaion wouldn't have ended up the way he did. Or, if he couldn't have stopped it, perhaps he could have prevented the situation that came together in RD. He certainly could have done something about Lehran.
Or did he agree with Lehran - was he aware of what "Sephiran" was doing? I don't think they ever answer that question. I want to say no, but there's no evidence either way that I remember.
But if you believe what they tell you about equality and/or non-hostility between the races at the time Ashera went to sleep, then it isn't Dheginsea's stubborn neutrality that is the problem - just a symptom, you could say. The problem started when Lehran's child was born, he lost his power, and then decided to hide his condition instead of sharing his knowledge with others.
It's not even the child, so much as his decision to run away and abandon Begnion. Regardless of his condition, his advice - his reputation as one of the founders of the country, and Ashera's trusted servant - could have changed the course of history. Would the senate have the balls to call laguz sub-human if Lehran was there? I don't think they'd have a following for that way of thinking. Not if he was a respected figure of the country's present, as well as its history. But it's the climate created by the senate's grab for power that allowed the Massacre to happen.
The heron refusal to acknowledge the Apostle is probably the other factor, and that can be traced directly to Lehran and Altina. If they'd been honest, if Lehran had stayed and guided his children, their nature wouldn't have been a point of contention between the government and the herons. Perhaps they knew what the Apostles really were. That seems a reasonable possibility to me. But the political rift wouldn't exist, I think, if their nature was public knowledge. Certainly live would've been easier for the Branded. That issue, the lie that laguz-beorc relationships were blasphemy, is actually almost peripheral - it's the product of their lie, not the cause of the problem.
Dheginsea helped Lehran and perpetuated the lie, but his inaction would've remained the same regardless of Lehran's decision. That's my reading of his character, anyway. He remembered the flood, remembered his promise to Ashera, and kept it.
Lehran's public presence would have allowed other nations to do the same. They're the only two left, and they had a responsibility to help the shorter-lived races to remember. Lehran abandoned that responsibility and gave up on Tellius at the very beginning, and the path the racial prejudices and conflicts took after that, while not directly his fault, leave him just as guilty of inaction, if not more so - because he could have advised them differently, and refused. He was too self-centered for that job.
I wonder if he thinks about it that way.
(He will now - in my stories, at least. :D)