If the underlying message in all major religions is to LOVE one another, why do we continue to allow hatred and violence to tear us apart?

CHRISTIANITY

Romans 13:8 – Owe no man any thing, but to love one another: for he that loves another has fulfilled the law.

ISLAM

Al-Baqara, Chapter 2, Verse 195 – And spend of your substance in the cause of Allah, and make not your own hands contribute to (your) destruction; but do good; for Allah loves those who do good.  

JUDAISM 

Leviticus 19,18 – Thou shalt not take vengeance, nor bear any grudge against the children of thy people, but thou shalt love thy neighbour as thyself

BUDDHISM

The Discourse on Loving-Kindness:

Like a mother protects her child, her only child with her life,
So with a boundless heart should one cherish all living beings.
Radiating kindness over the entire world:
Spreading upwards to the skies and downwards to the depths,
Outwards and unbounded, free from hatred and ill-will.

HINDUISM

Bhagavad Gita 6.28-32 – If I speak in the tongues of men and of angels, but have not love, I am a noisy gong or a clanging cymbal. And if I have prophetic powers, and understand all mysteries and all knowledge, and if I have all faith, so as to remove mountains, but have not love, I am nothing. If I give away all I have, and if I deliver my body to be burned, but have not love, I gain nothing.