I wager that if one were to survey just about any given set of people, they should discover that very few of them would define themselves as ‘materialistic rationalist.’ Except amongst high-brow intellectuals, such philosophical stringency seems quite unnecessary. Indeed, why wouldn’t plain old ‘atheist’ or ‘agnostic’ do?
Incidentally I find materialistic rationalism to be a rather brave position to adopt. It is brave because it takes a certain amount of courage to bind oneself – exclusively – to what is verifiably true. We can only know what we know, but only the rationalist seems to know this; he says “I acknowledge my ignorance for what it is.” This is essentially the Socratic method.
However, it is clear that many reserve some hope of attaining gnosis by means of revelation. It is a primal obsession to know everything, and religious belief systems offer ample opportunity to learn what would otherwise remain opaque by the constraints of circumstance, and the universe’s unyielding laws. Hence the believer rhetorically enquires: “Why would anyone purposely give themselves to so narrow minded a worldview as the materialistic (bad word) rationalist?”
As far as atheism and agnosticism are concerned, well these are not actually worldviews whatever, but simply the denial of – or the attitude of neutrality regarding – a theistic worldview. As Sam Harris famously put it, “I think that ‘atheist’ is a term that we do not need, in the same way that we don’t need a word for someone who rejects astrology.”  In other words, it is merely a statement that one will not be seduced by the form of escapism which Holy Books (like all works of fiction) promise us, that we may not have to contend with reality.
Rather I do believe there is something to be said about the act of affirmation in favour of Truth, so in that regard I share the view of the religious, though that is where the similarities end. Unlike them I also hold that we must respect Truth, and learn to know her face. One is given to seeking her out in those crevices into which insight has yet to peer, but we should not forget that where we do find her, she will be as clear as day. She has no confidantes among Homo sapiens with whom to divulge her secrets. She does not bend to any will, nor abide by any law – not secular, not religious; so, if she happens on occasion to veil her countenance, it is not intentional on her part.
We must therefore be patient. What we define as the material world is simply the world through which Truth has revealed herself. We should not appeal to what lies outside of it, no matter how tempting.
It is only rational.