The popular myth that Paul was deceptive is expressed by writers such as Gerald Sigal, Michoel Drazin, and Beth Moshe:
In his overriding desire to convert the masses to his beliefs, Paul is guided by the dubious assumption that the end justifies the means...The use of deception, by himself or others, in order to bring about belief in Jesus did not disturb Paul.
Gerald Sigal, The Jew and the Christian Missionary: A Jewish Response to Missionary Christianity (New York: Ktav, 1981), p. 272. See also p. 290: "he considered deceit and pretense valid means for achieving his goal.
[Paul] openly advocated 'pious fraud.'
Michoel Drazin, Their Hollow Inheritance: A Comprehensive Refutation of the New Testament and Its Missionaries (Jerusalem: Gefen Publishing House, 1990), p. 18.
"We feel we should demonstrate the unreliability of the man who actually formulated the break away from Judaism by the early Church...Now see who he is, by his own words. He admitted using trickery and deception to gain his ends."
Beth Moshe, Judaism's Truth Answers the Missionaries (New York: Bloch Publishing Company, 1987), p. 212.
The New Testament passage in question that supposedly reveals Paul as a deceiver is First Corinthians 9:20-22:
To the Jews I became like a Jew, to win the Jews. To those under the law I became like one under the law (though I myself am not under the law), so as to win those under the law. To those not having the law I became like one not having the law (though I am not free from God's law but am under Christ's law), so as to win those not having the law. To the weak I became weak, to win the weak. I have become all things to all men so that by all possible means I might save some.
Far from being deceptive, Paul, when he wrote the passage from First Corinthians, was drawing on Jewish communications methods of his day. Like other Jewish leaders, Paul was simply being a good teacher and communicator. What Paul sets forth in First Corinthians is not a principle of deceit and expediency, but a principle of communication such as was taught and practiced by Hillel and others. Craig Keener, Professor of New Testament, Hood Theological Seminary, places First Corinthians 9:20-22 firmly within a Jewish context.
Some Jewish teachers, like Hillel, were similarly accommodationists, to win as many as possible to the truth.
The IVP Bible Background Commentary (Downers Grove IL: InterVarsity Press, 1993), p. 472.
Similarly, David Daube, a Jewish Professor of Law at University of California, Berkeley, wrote at length about Paul's principles as found in First Corinthians 9:20-22. The following is taken from a much longer chapter, "Missionary Maxims in Paul," which is found in Daube's book The New Testament and Rabbinic Judaism:
[This idea is] taken over by Paul from Jewish teaching on the subject: the idea that you must adopt the customs and mood of the person you wish to win over....
First, for the idea of accommodation. Let us start from a passage in I Corinthians [Daube quotes First Corinthians 9:20-22].
This attitude had formed part of Jewish missionary practice long before Paul. Two Talmudic illustrations of Hillel's work are relevant: he accepted into the fold a gentile who refused to acknowledge the oral Law, and he accepted another who refused to acknowledge any Law beyond the most fundamental ethical principle [b. Shabbat 31a and Avot de-Rabbi Nathan 15]...At the decisive moment of conversion, he fell in with the notions of the applicant and declared himself satisfied with recognition of the written Law or a single, basic moral precept....
Hillel, we might put it, was made all things to all men, that he might by all means save some.
[Hillel had a saying] which may chiefly contemplate relations to outsiders [Tosefta Berachot 2.24]: "Do not appear naked, do not appear dressed, do not appear laughing, do not appear weeping -- as it is said, A time to weep and a time to laugh, a time to embrace and a time to refrain from embracing [Ecclesiastes 3:4f.]....
In the treatises Derekh Eretz Rabba and Derekh Eretz Zuta, we meet with descendants of Hillel's maxim. The former contains this paragraph: "A man should not be joyful among the weeping, nor weep among the joyful, nor wake among the sleeping, nor sleep among the waking, nor stand among the sitting, nor sit among the standing--the principle of the matter is, A man should not make different his mind from that of his fellows and the sons of men." The passage from Derekh Eretz Zuta is substantially the same, with two exceptions: there is a further pair of warnings, "nor should he read Scripture among those reading Mishnah, nor Mishnah among those reading Scripture," while the summing up runs, "A man should not differ from the usage of the creatures."
These paragraphs are evidence that Hillel's idea was taken up by others and lived on....
[It is] rather probable that Hillel did intend his maxim [cited above from Tosefta Berachot 2:24], which refers to behaviour among strangers, for use in missionary activity.
For another thing, in establishing the Jewish antecedents of Paul's plan, we need not rely exclusively on Hillel and sayings derived from him. In the Letter of Aristeas, the king asks how he might meet with acceptance when travelling abroad; and the answer opens, "By becoming equal to all," pasin isos ginomenos. As it stands, it is advice for a traveller -- a traveller who wishes to find favour with his hosts. Moreover, the term "equal" has a political sense: the traveller is a king, and he is advised to make light of his rank. None the less it may be assumed that, as early as the time the Letter was composed, this was also a slogan of proselyte-makers. The author of the Letter himself was a Jewish propagandist.
Paul, when he wrote the passage from I Corinthians quoted at the beginning, was drawing on a living element in Jewish religion.
David Daube, The New Testament and Rabbinic Judaism (Salem, NH: Ayer Company, Publishers, Inc., 1992, © 1956, 1973), pp. 336-41 passim.