I understand blue hair a bit but I lean more towards the MC.
In a real life scenario where someone I love is in danger, I'd wager my life for that 0.0000000001% chance to save them but I wouldn't do it for someone I just met. Then again, I've never been in love so I don't know how compelling of a feeling that is but aside from close family members, I don't see myself doing that for someone else.
The motivation for mr blue hair isn't bad but dashing in without any plan is stupid especially since he has a strong family that apparently rivals their current enemies (I think ? The way I understood it is that the strongest people in his clan/sect should rival the strongest people in the enemy's powers) but then again, his sect might not agree to help and all that shit but he needs to think of something. I acknowledge that this method isn't the best since him wanting to protect that girl might result in many more deaths if 2 strong clans clash but if he is that determined, he needs to do something.
I see the MC's point of view if he were to run away and not do anything or if he were to help after devising a plan about it . If he ran away then it's understandable because he is 10000000% going to die if he went there so saving himself isn't evil ro anything. He never promised the girl he'd save her either.
If he devises a plan to save her then all the best and on that note, our guy is changing slowly but surely. I knew he would start changing when he faced the bird beast and said something along the lines of "they're my people" or "their lives are mine" or something like that. I knew he'd no longer think of them as tools