In the cover article of the most recent issue of Biblical Archaeology Review (March/April 2007), "The Mystery of the Nechushtan", Hershel Shanks presents the theory of Kristin Swanson (originally published in Catholic Biblical Quarterly 64 (2002), p. 460, "A Reassessment of Hezekiah's Reform in Light of Jar Handles and Iconographic Evidence"). I do not have access to this article so my very brief critique may not apply to her actual theory - just H.S.'s presentation.
H.S. writes, "Scholars have often speculated that Hezekiah destroyed the Nechushtan because it had come to be worshiped in the Temple and hence was as objectionable as the other cultic objects condemned in 2 Kings 18:4." The problem, very simply stated, is that this is not a scholarly speculation - it is the second half of the verse in 2 Kings. Even more perplexing is the fact that when H.S. cites this verse he leaves out the second half, which he seems to consider scholarly speculation. This is the verse with the part that he left out in bold.
ד הוּא הֵסִיר אֶת-הַבָּמוֹת, וְשִׁבַּר אֶת-הַמַּצֵּבֹת, וְכָרַת, אֶת-הָאֲשֵׁרָה; וְכִתַּת נְחַשׁ הַנְּחֹשֶׁת אֲשֶׁר-עָשָׂה מֹשֶׁה, כִּי עַד-הַיָּמִים הָהֵמָּה הָיוּ בְנֵי-יִשְׂרָאֵל מְקַטְּרִים לוֹ, וַיִּקְרָא-לוֹ, נְחֻשְׁתָּן.
4. He removed the bamot and broke the matzevot and cut down the asherah; and he ground up the bronze serpent that Moshe made, for up until those days the Children of Israel would offer incense to it, and he called it (or, it was called) Nechushtan.
Without reading the second half of the verse how did he know that the nachash haNechoshet was called Nechushtan? This said, I did enjoy the article.