It is very simple really. Both Jews and Muslims deny the Trinity. While hatred of the Jews began with the Catholic Church about 20 centuries ago, Christians in Europe would no doubt have hated Muslims too if they had been around, because they also deny the Trinity. The Unitarians were also horribly persecuted.
It is very easy for an intelligent and educated man familiar with Christian doctrine to mock and attack the veracity and its purpose of the Trinity and very difficult for Christians no matter how clever and educated to defend it.
The Unitarians were also persecuted by Trinitarians. One can understand why one might get angry with someone else about some belief of moral consequence, but to persecute someone else because he believes God is one rather than your three is insane, wicked and primitive.
No wonder the Catholics decided to teach these pesky Jews and Muslims a lesson through the Inquisition.
It has always the Christian Church's position that if one did not believe in the Trinity one is not a Christian and shall not be saved, for only Christians go to heaven and bad Christians can be forgiven if they believe in the Trinity and repent.
The bargain the early Catholic Church struck with early Christians was that if they accepted the Trinitarian "explanation" of Christ's divinity they would go to heaven if they were regular church-goers and repented of their sins.
Is there a moral dimension to this belief? Methinks not. It is clearly a CORRUPT bargain. But there are those who would even now support this lie, because they must feel at all costs different and better than Jews and Muslims even when reason must tell them that Christianity is clearly an inferior religion, and inferior because it is cowardly, hypocritical, irrational, fanatical and fundamentally unjust.
The Enlightenment only came about when Western man decided to take the Bible with a very large pinch of salt.
The Koran on the other hand has rules that are easy to understand and a very low entry threshold. Even a non-Muslim can say the shahada without doing any injury to his beliefs. You don't need to be a Muslim to recognise that, if you believe in God, then you would necessarily believe that there is no God but God, and that Muhammad is the messenger of this God.
Compare this to the farrago of nonsense that is the Nicene creed and the 21st century identification of Christianity as the religion of the militaristic NATO members whose nations are riddled with paedophiles, feminists and single mothers wanting to promote gay marriage all over the world. http://thevoiceofreason-ann.blogspot.co.uk/2014/06/does-archbishop-of-canterbury-think.html
Who would be a Christian now, except one who is very stupid, chauvinistic and very stubborn who will do anything, including deny the truth and refuse to discuss it, in order to pretend that the religion of his ancestors must be the best simply because it is the religion of his ancestors? This is so even when he has seen how utterly useless it now is in maintaining the morality of his people because of its corrupt priesthood who regard the Church as a source of income and employment while they subvert its teachings at the State's behest.