I wish to encourage actor Liam Neeson not to renounce his Catholic faith to become a Muslim.
In his book, 'The Great Christian Heresies', Hilaire Belloc classifies Islam as a Christian heresy. The foundation of Mohammed's teaching is Catholicism, which he took and simplified to suit his own personal convictions.
His central heresy is a full denial of the Incarnation. He taught that our Lord was merely a prophet; a man like other men.
The Mohammedan movement was essentially a 'Reformation', and we can discover numerous affinities between Islam and Protestant Reformers on images, on the Mass, on celibacy etc.
This radical, individualistic, decentralisation of truth, when followed to its logical conclusion, culminates in moral relativism -- the belief that all religions are equally valid.
This is simply not a rational belief. It is contradiction, for example, to claim that God is, at once, both a Personal Being (as Catholics hold) and a non-personal entity (as the Buddhists claim).
At the heart of Mr Neeson's confusion, I would suggest, is the desire to want to measure the truth of his Catholic faith by modern society's individualistic standards.
Such people mistakenly believe that divine Revelation must adapt itself to the current mentality in order to be credible, instead of the current mentality converting in the light that comes to us from on high.