Murphy, rather emotionally, rebutted them with a familiar story about Jesus.
There are two problems with Bob's response: the story isn't about gays, and it never happened.
The story is, of course, the woman taken in adultery from John 8. Bob bases his argument on Jesus's dictum "let him who is without sin cast the first stone." This is a story about the law on adultery not homosexuality. Perhaps this dictum would apply to the law on homosexuality too, but then it would presumably apply rather more broadly than Murphy might like. Murder? Rape? Would Jesus tell murderers and thieves to go and sin no more? Is there any criteria we can use to decide? This is a common problem when playing WWJD.
But there is a more serious problem with Bob's pericope (to use some jargon). It never happened. It's a late invention, inserted into John centuries after John was redacted. It does not occur in <i>any</i> early manuscripts of John. It does not occur in the <i>best</i> manuscripts. It does not occur in early discussions of John. It is not cited in early discussions of adultery. It is not mentioned by any early church writers. Its language does not match John. It breaks the natural flow of the surrounding text. It is called late by medieval writers. It presents an implausible picture of how Jewish law was carried out. It presents an implausible view of the Pharisees. It simply does not belong in John. It's a late invention.
That's not just my opinion, it's the scholarly concensus. Even my Crossway Bible has a note about the passage. Perhaps Bob should read his Bible ...
Here for example is Bruce Metzger on the passage:
The evidence for the non-Johannine origin of the pericope of the adulteress is overwhelming. It is absent from such early and diverse manuscripts as Papyrus66.75 Aleph B L N T W X Y D Q Y 0141 0211 22 33 124 157 209 788 828 1230 1241 1242 1253 2193 al. Codices A and C are defective in this part of John, but it is highly probable that neither contained the pericope, for careful measurement discloses that there would not have been space enough on the missing leaves to include the section along with the rest of the text. In the East the passage is absent from the oldest form of the Syriac version (syrc.s. and the best manuscripts of syrp), as well as from the Sahidic and the sub-Achmimic versions and the older Bohairic manuscripts. Some Armenian manuscripts and the old Georgian version omit it. In the West the passage is absent from the Gothic version and from several Old Latin manuscripts (ita.l*.q). No Greek Church Father prior to Euthymius Zigabenus (twelfth century) comments on the passage, and Euthymius declares that the accurate copies of the Gospels do not contain it.This tale is central to Murphy's idea of a kinder, gentler Jesus, and that is a major theme on his blog. Bob gets testy when I point out the problems, but he has never responded.
When one adds to this impressive and diversified list of external evidence the consideration that the style and vocabulary of the pericope differ noticeably from the rest of the Fourth Gospel (see any critical commentary), and that it interrupts the sequence of 7.52 and 8.12 ff., the case against its being of Johannine authorship appears to be conclusive.