I noted a few weeks ago I read The English Civil War. This passage struck me:

All beholders, said a Dorset draper visiting London, shed tears. There were ironies in all this hero-worship. According to the Catholic Sir Kenelm Digby, the godly [Puritans] were, hilariously, keen to gather relics of the martyrdom, the bloody sponges and handkerchiefs: 'you may see how nature leads men to respect relics of martyrs'.

The key point is to note that the Puritan Protestants indulged rather quickly in the same idolatry for which they upbraided the Catholics! In the chapter on "The War Against Christmas" the proto-Benthanmite inclinations of Puritan rationalists is on full display, as the divines inveigh against saints days and other accretions upon the plain and simple Biblical faith, and not for the first time place the quasi-pagan festival of Christmas in their sights.

And yet let us recall the ascetism on display in the Letters of Paul, and the "unnatural" lionization of celibacy common in the early Church (and shared with pagan intellectuals in the Neo-Platonic tradition), which persisted down to the days of the Reformation. Though the Protestants rebelled against human nature, the love of the beautiful, elegant and the mixing of the sacred and material, the bleeding of the divine into the corporeal, they were also willing to concede to the necessity of human nature when it came to carnal inclinations.

An important consideration is understanding particular cultural manifestations of human universal tendencies, whether it be toward religion, social stratification or art, is that they tend to be "canalized" by our cognitive biases toward particular optimal (and familiar) states. Nevertheless, there is variation in human predispositions, and I believe that one of the tensions common in "elite" religious traditions is that the professionals who shape the exoteric formulation of the religious doctrine and the proper forms and rituals are often somewhat atypical in their emphasis on rationality and logical consistency, and their distance from common tastes and inclinations. During initial stages of cult formation, whether it be "primitive Christianity," or the initial stages of the Muslim community, a self-selected Elect establishes the norms and conventions which define "orthodoxy" and "orthodpraxy." But over time as the religion spreads and succeeds in being a mass movement these idealized forms must compromise with the reality of human religious sentiment, and the canalization toward recurrent religious motifs and forms found in all cultures becomes ever more powerful. In short, religions may be initated by common and recurrent socio-historical forces (e.g., a messianc leader taking advantage of economic dislocation), but they eventually converge upon common cultural truths.

In regards specifically to the tendency for religions to throw up a cult of relics, and a counter-tendency of rationalist "Puritans" to denigrate this sentiment, consider a object precious to your beloved. Even an atheist materialist, who sees in the universe around himself simply organized atoms, would be hard pressed to deny the sentimental value in keepsakes once in the possession of those who have now passed from this world. Fundamentally it is these banal psychological tendencies which can transmute into imbuing a bloody shroud with divine miasma.