And that scene was unnecessary. It's a very good story with complex plot and ended with a typical yaoi trope. That was almost perfect if not for that scene really, I wish I could also erase my memory of reading that.
I completely agree with you-
Ignorance is not bliss, it's a vanity, the price of which only a few can afford to pay.
And yes I hated the end but I guess the author didn't want James to be like Rugal in terms of his actions which he might have been like had he killed him though the main essence of the whole story was Revenge- one which failed to be achieved. What was even more awful was the fact that Rugal did not seem to repent any of his past disgusting actions which made giving him a redemption of sorts by letting him live utterly stupid.
It just felt that there was a character development then boom back to zero. Overall the story is very well done except for the end part. It is just frustrating to go back to being ignorant and all that shit even though it is what the author would like to convey that sometimes it's better not knowing the truth. But in this case it just doesn't work for me.