You always get to keep your beliefs. Your beliefs are conditioned by no one but yourself. But if you fight against others and take up arms against them then obviously you don't want peace. But it is how we act on our beliefs that is important. For instance I can believe homosexuality is improper but still be very kind and loving to those who practice it without harming or hurting anyone.
It is up to each of us to have an attitude that is conducive to peace, that is if we want peace. You have to plant a tree, water it and cultivate it to get fruit so too with peace. It won't just happen unless we are more tolerant and forgiving and willing to overlook humanity's weaknesses and shortcomings.
To have peace we all need to make an effort not just governments.
So if we can stop judging each other and just accept each person as a fellow human being without preconditions then we could have peace but with all sorts of preconditions peace is impossible.
So if we all believe that humanity is one we can have peace if that is our major belief. We can not agree on many matters but if we all believe we are fellow humans we can still have peace.
I think we don't see eye to eye here! See, I think one can want peace in principle but still be prepared to fight/take up arms against others if the occasion demands it. Peace is not for me the be all and end all.
Moreover, I'm not sure I believe that humanity really are one in any important sense. I'm not sure that the fact that we belong to the same species really matters all that much. I think there are more important considerations.
But thank you very much for the conversation!