A better qustion than that posed in the article shall be, why would a female sibling of a US Supreme Court Justice seek to become an Episcopal priest, write guidance for women at a seminary, and now propose Christ was illegitimate son of Joseph.
The answer to this second query is more obvious when one understands the doctrines of the Immaculate Conception, the Old Sin Nature, Kenosis, and Spiritual Gifts.
The very lineage of Christ is consistent through the line of Mary, wheras the line of Joseph was broken when a king of Israel reblled from God leading Israel through 5 stages of discipline and their destruction. Nevertheless, God's Word prevails and our Lord and Savior Christ Jesus was born through Mary.
Some rigorous studies also suggest that the old sin nature, or natural man, passes sin from generation to generation, if by no other method, then surely by genetic methods from the male chromosomes. This in part is one reason why all humans are borne dead in the spirit since Adam and Eve, except for the second Adam, Christ Jesus. His conception, an immaculate conception, allowed for a man to be borne pure in body, soul, and spirit. In fact, the only man ever so borne after Adam, hence the only possible true pure Lamb available as an offering for the propitiation of sin of all mankind, thereby a God provided solution to His integrity and grace, allowing a method for man to have a relationship with Him while He retained integrity.
IMHO, for those who might consider the existance of Illuminati, occultic groups, and hidden agendas, her position provides powerful evidence consistent with conspiracy theorists that there are circles within human authority that seek to counterfeit God's plan for their personal agendas.
She's just a poor ignorant modernist who went through a heretical Episcopalian seminary. She never learned Hebrew or Greek (it's no longer required in any ECUSA seminary AFAIK - there is a conservative Anglican seminary in the U.S. but the ECUSA will NOT ordain any graduate from it). Her professors poured modernist, worldly, Higher Criticism poison into her ears. She may well have never actually sat down and read the Bible - just the Cliff's Notes version in her approved textbooks.
I haven't seen an ECUSA priest (or "priestess") under the age of 50 who has received a solid theological education. I used to argue with our rector and had an unfair advantage because I could read Greek and he didn't have a clue. (I was a cradle, indeed a sixth generation, Episcopalian until GC 2003. Now I am a Catholic.)
Like AnAmericanMother says, applying Occam's Razor gets you a simpler explanation: Rev. Chloe's just being either incredibly stupid or deliberately provocative - or, since she's a leftist, probably both.
(Certainly Slate's intention was Judeo-Christian-bashing: the other articles in the Christmas issue, according to the web page, were "Bring Out the Kwanzaa Kinara", "Who are my mother and my brothers? - The Gospels don't preach family values", "The Maccabees and the Hellenists - Hanukkah as Jewish civil war", and "Eluding Happiness - A Buddhist problem with Christmas.")
Can't these people come up with some new heresies for once? Heck, even Marshall Applewhite of the Heaven's Gate Cult invented a few new ideas. And he was just a sexually confused drifter who'd chopped his own nards off! C'mon Chloe, you can do better than that!