Why does the speaker, presumably Wordsworth, wish to remain a pagan?
Wordsworth does not say he would like to remain a pagan but that he would rather be a pagan than be a materialistic modern man without any religious belief, engrossed in making money and buying things. Evidently Wordsworth felt that belief in God stemmed from being inspired by the wonder and beauty of nature, and that by losing his belief in a supreme being modern man has lost contact with nature as well. Many people have had religious experiences inspired by perceiving the awesome spectacle of the stars scattered across the universe and by other such inspiring sights. Wordsworth was one of them. In this sonnet he focuses on the beauty of the ocean and the lifelike qualities of the winds. It was characteristic of Wordsworth that he imagined himself addressing an audience. He was thinking that he was getting too deeply engrossed in making money and spending it on necessities for his growing family; but he saw that what was affecting him was common to men of his time in general.
There are other poets who have been described as "solipsistic" who do not feel obliged to address a reader or an audience or anyone in their poems. They talk to themselves, which often makes them difficult if not impossible to understand because they feel no need to explain a lot of things they already know themselves. Solipsism is the notion that only the self exists. Everyone we know is only a figment of our own imaginations, as is everything we perceive and everything that happens to us. Wordsworth always sounds like a man who might have been a minister at an earlier time but who lost his faith in the established church and was looking for a new religion through revelations inspired by nature, just as the prophets of the Bible had experienced revelations inspired by nature, and probably just as all religious revelations had been inspired in a similar manner. When he speaks of being a pagan "suckled in a creed outworn," he seems to be reflecting that his own religious creed taught to him in childhood is also outworn.
The sentiments expressed in "The World Is Too Much with Us" seem quite similar to those expressed by Matthew Arnold in "Dover Beach." In that famous poem the speaker, presumably Arnold himself, is also looking out over the sea at night. He begins with the words
The sea is calm tonight.
The spectacle makes him think about religion and about pagan times. In one stanza he seems to echo Wordsworth's sonnet.
The Sea of Faith
Was once, too, at the full, and round earth's shore
Lay like the folds of a bright girdle furled.
But now I only hear
Its melancholy, long, withdrawing roar,
Retreating, to the breath
Of the night-wind, down the vast edges drear
And naked shingles of the world.
The vision that the speaker, presumably Wordsworth, presents in the poem is one in which conformity and social acculturation in all of its forms have created a corrupted vision of what can be. This vision is where Wordsworth wishes to be a pagan. In his most fundamental of believes, Wordsworth made the argument that spiritual identity is something where the force of social conformity within it creates more harm than good: “the study of human nature suggests this awful truth, that, as in the trials to which life subjects us, sin and crime are apt to start from their very opposite qualities.” For Wordsworth, this is seen in the "getting and spending" a condition in which traditional notions of religion have lost their meaning.
It is in this where Wordsworth would rather be deemed as a "pagan" and believe in something authentic and more valid as opposed to something that rings hollow with a reality in which "we have given our hearts away." Wordsworth sees the current state of spiritual identity as one that has not done much to stop the corrosion of individual values. Wordsworth finds it acceptable to avoid this "sordid boon," even if he is called a pagan for doing so. It is in this rejection of traditional ideas of spiritual identity where Wordsworth can be seen as advocating being a pagan.