So I decided to do Shura Ending in my NG+, coincedentally also decided to send Kotaro to abandoned dungeon because I want to see doujin chain quest, and needless to say I'm pretty disgusted with myself and feel like a sliver of my humanity just lost. But I have some random afterthoughts about Shura.
First I was no monk, but I've read a good deal of buddhism lore texts (Asian here), and to my knowledge – shura or Asura: are not demons at all, they are considered Demigods, having powers equally to Buddha himself. A piece of texts I've read on secondary school (too – too long time ago) but I remember it well because I was so impressed by it – loosely translated "human's nature is goodness, and to do goodness is to come near your nature, and achieving Nirvana. But if one's nature is destruction – and they aimed to do as their nature's will, then they also can become a greater being – having powers equal to Buddha".
As such, if it were true, then the Scuptor can never become Shura – destruction is not his nature, and Isshin cut his arm off's action was not to not let him become Shura, but to not let him become Demon of Hatred, to calm down Scuptor's bloodlust. And when Interior Ministry's army attacks Ashina, he could not contain his hatred no more – his hatred for invaders, so he becomes Demon of Hatred because he wanted to protect his country, maybe that's why Ashina could hold out the Interior's army for so long: because the Scuptor was ravaging Interior Ministry's army. So destruction is not of his nature – all he wanted is protecting his country, all he wanted is peace, is for his country to keep its traditions.
And for Wolf, he can become Shura because… he was born a creature of destruction, he's an orphan born in the time of war, he has never seen peace, since he was born, all he's seen is war, is destruction, his hatred is pure, destruction is his nature. That is his sadness – he's never known better.