Silk has an interesting argument, but I find it utterly unconvincing. First of all, I find his claim that using they to refer to God does not undermine monotheism not very convincing. Silk points out that in the Hebrew Old Testament one of the words used for God is Elohim, which is plural in form. This word is distinct from God's personal name, Yahweh, which is singular in form. Since the original language of the Bible uses a plural noun to refer to God, shy not use a plural pronoun? The problem is that, according to my understanding, this use of a plural form--Elohim--in Hebrew to refer to God is an example of the "plural of majesty." That is to say, in Hebrew a noun might be made plural to emphasize the majesty of what it refers to. However, English lacks such a concept as "plural of majesty," so the use of a plural pronoun in English to refer to God would not really be analogous to using a plural noun to refer to Him in Hebrew.
Second, in the both the original Hebrew of the Old Testament and the original Greek of the New Testament, God is consistently referred to with masculine pronouns and nouns. Silk himself informs us that "in the Hebrew Bible, God is addressed with the second-person masculine pronoun 'attah'". Moreover, in the Greek of the original New Testament, the word for God--Theos--is clearly masculine in gender. For example, in John 1:1 we read Theos en ho Logos--"God [masculine] was the Word [masculine]." In Christian belief, the Bible, though authored by human beings, was directly inspired by God. Thus, it would appear that God intends for us to refer to Him using male nouns and pronouns--for some reason we cannot be certain of--even though He transcends gender. To be fair, my impression is that Silk would not consider himself a theologically orthodox Christian (I note that he writes god instead of God, something an orthodox believer would not do), so he might not find this a compelling argument, but I certainly do.
Third, I am not swayed by Silk's contention that changing the pronoun with which we speak of God from He to they is of no more significance than changing the pronoun with which we address Him from Thou to You. These are not analogous situations. Neither thou or you imply gender (or a lack thereof)--they merely signal singular or plural. However, not only do he and they imply differences in number, they also signal differences in gender. Thus, Silk's analogy breaks down.
In short, Silk's argument for replacing He with they when referring to God is not really convincing at all, if we take the time to analyze it carefully from both a linguistic and a theological perspective. Ultimately, his proposal to change the way we refer to God is really an effort to change the way we perceive God, distorting what God Himself has revealed to us about His nature. This is quite a dangerous thing to do.
Image of Holy Bible from Wikimedia Commons