I find it interesting that the term anomia "lawless, without law" is found only in Matthew in the gospels; it apparently is a Matthean-specific term. It is found in Pauline writings (cf. Romans 4:7, 6:19; 2 Corinthians 6:14), and curiously in 1 Corinthians 9:20-21 Paul uses the related word anomos to refer to Gentiles who were not hupo nomon "under the [Mosaic] Law," and declares himself as "not being myself under the Law" (mè hòn autos hupo nomon) when he preaches to the Jews who are under the Law, and specifically being "lawless" (hòs anomos) to those "who are without Law," the Gentiles, to bring them instead under the "Law of Christ" (ennomos Khristou). This appears to be a precedent for the Matthean use of anomia to critique (Pauline) followers of Jesus who do not observe the Torah.
I like your connection between Pauline Christianity's rejection of the Torah and the loss of community love in Matthew 24:12, for Matthew has love as the cornerstone of Torah observance and the entolais "commandments" (22:35-40), and it is a dominant theme in Jesus' teaching (5:45-46, 6:24, 10:37, 19:19). There is an interesting link here with the Johannine writings. 1 John 2:3 says that we know Jesus "if we keep his commandments (entolas)," and 4:21 (cf. 3:23) says that "he has given us this commandment (entolèn): Whoever loves God must also love his brother," the primary commandment being love. Interestingly, 1 John 3:9 says that "no one who is born is God practices sin, because his seed abides in him and he cannot sin," and v. 23-24 show that those who "love one another" and "keeps his commandments" are those who abide in God, whereas those who do not love "practice sin" (poiòn tèn hamartian), and "everyone who practices sin also practices lawlessness (anomia), for sin is lawlessness (anomia)" (3:4). Like Matthew, there seems to be a connection between agapè "love" and keeping the entolais on the one hand and the anomia that results from the lack of agapè or entolais observance. 1 John also seems to reflect the same social circumstance discussed in Matthew 24; the work critically discusses the antikhristoi who are born of the Devil, who do not show love towards their brethren, and who had originally been members of the religious community (2:18-19, 22; 4:3), and 1 John 2:17, 3:24 is reminiscent of Matthew in its focus on works: "The one who does the will of God abides forever...The one who keeps his commandments abides in him, and he in him." This is not to say that 1 John necessarily endorsed the same Jewish-Christian notion of Torah observance as Matthew (for the term "commandment" clearly has a different meaning for the Johannine community), but the broad outlines appear quite similar, particularly in the linkage between anomia and the lack of agapè and entolais observance in a so-called Christian group the author's community saw itself in opposition to. Similarly, in the gospel, Jesus says, "If you love me, you will keep my commandments....He who does not love me does not keep my words" (John 14:15, 24).
If Griffith is right in his analysis, I think the connection between Matthew and 1 John, John may be in the critique of ethnic Jews who had become disciples (cf. 1 John 2:19, "[they] went out from us") but who slid back into Pharisee Judaism, renounced their faith in Jesus Christ, and even took part in the persecution of Christians in the synagogues. This seems most clear in John 8:31-59, which Mark Stibbe (John's Gospel, published in 1994) characterizes as "satirizing apostasy ... those who start on the road to discipleship, but who give up when the going gets tough" (p. 124). Verse 31 describes them with the perfect participle pepisteukotas as "those who had believed in Jesus (e.g. but do so no longer)," and the language in this passage has the most parallels with 1 John than elsewhere in the gospel (including characterizing such people as "children of the Devil"). John 16:2 goes on to say that "they will make you outcasts from the synagogue, but an hour is coming for everyone who kills you to think that he is offering service to God," a pasage which best reflects Pharisee persecution and which parallels Matthew 10:17-23. Justin Martyr (Dialogue, 47.4) mentions Christian apostates as those who "once professed and recognized that this is the Christ, and for some cause or other passed over into the life under the Law, denying that this is the Christ (arnesamenous hoti houtos estin ho Khristos)," which compares well with the statement in 1 John 2:22: "Who is the liar but the one who denies that Jesus is the Christ (arnoumenos hoti Ièsous ouk estin ho Khristos).
Another thing to note which has been neglected up to now is the whole eschatological and apocalyptic flavor of anomia in Second Temple Judaism. The Testament of Dan 6:6 refers to a final "period of iniquity" (en kairò tès anomias) that precedes the coming of the Messiah and 2 Thessalonians 2:3 refers to a "man of lawlessness" (anthropos tès anomias) as the ultimate apostate that rebels against God at the time of the end. Barnabas 4:9 admonishes: "Let us be on guard in the last days, for the whole time of our faith will do us no good unless now, in the age of lawlessness (tò anomò kairò), we resist as well the coming stumbling blocks," and 15:5 states that "when his Son comes, he will destroy the time of the lawless one (kairon tou anomou) and will judge the ungodly and change the sun, moon, and stars". There are also parallels in the Apocalypse of Abraham 24:5, the Apocalypse of Elijah 3:1-13, 5:10, the Ascension of Isaiah 2:4, 4:2, and the Sibylline Oracles 3.69. It would thus be good to recognize that we are dealing with a standard apocalyptic motif here, which might be sufficient to explain the occurrence of anomia in the apocalyptic portion of Matthew (ch. 24) -- rather than the use of the term elsewhere in the gospel, where it pertains more to Torah observance. It is quite possible, of course, that the author conceived that Pauline Christians and the Pharisees were themselves rebelling against God and were thus "wicked" and "men of iniquity," but the apocalyptic genre of ch. 24 might be enough to warrant such a statement regardless of the community's views toward these groups. I should also note that there is a close parallel to Matthew 24:12 in the Didache apocalypse (which is similarly Jewish Christian), which reads as follows:
"For in the last days the false prophets (pseudoprophètai) and corruptors will abound, and the sheep will be turned into wolves, and love (agapè) will be turned into hate (misos). For as lawlessness (anomias) increases (auxanouses), they will hate and persecute and betray (paradòsousi) one another. And then the deceiver of the world will appear as a son of God and will perform signs and wonders, and the earth will be delivered into his hands, and he will commit abominations the likes of which have never happened before" (Didache 16:3-4).
"And at that time many will fall away and will betray (paradòsousin) one another and hate (misèsousin) one another. And many false prophets (pseudoprophètai) will arise, and will mislead many. And because lawlessness (anomian) is increased (plèthunthènai), most people's love (agapè) will grow cold" (Matthew 24:10-12).
The reference to sheep and wolves is interesting in the passage, as it forms a link with Matthew 7:15-23 which refers to the "false prophets" (pseudeprophètai) "who come to you in sheep's clothing but inwardly are ravenous wolves" who are also "workers of lawlessness (anomian)". The Didache passage also makes clear that ones who lose their love are those who were formerly "sheep".