Disclaimer: I'm not publishing a book here. So I don't provide extensive documentation. Sorry. You can go do some research and see what you think.
(You can easily find this man's websites by searching on his name.)
Although Rabbi Singer brings up some difficult topics (i.e., some points at which there are either difficult concepts or evidence that is hard to process), he fails to understand Christianity or to take its evidences seriously. He also fails to consider different interpretations of some critical aspects of the New Testament itself.
For example, all [or, at least, "all that I spent time to read"] of his arguments against the Trinity are straw-man arguments. That is, his arguments don't even address what orthodox Christianity teaches about the Trinity. His arguments consistently fall into one of two categories: (1) against a polytheism of 3 "gods", (2) against the concept that God is capable of somehow limiting Himself -- Singer's conclusion being that since Jesus possessed human limitations, it is impossible for Jesus to be the one true God. But of course, neither of these sorts of arguments actually addresses the Christian concept of one God who is a Trinity, and who chose to somehow become a full human being. (The concept of God being capable of self-limitation is quite a different thing than the concept of the Trinity, although there is some overlap when we consider Jesus' humanity.)
More generally, Rabbi Singer fails to take the evidence of the New Testament seriously. This is not surprising, given his a priori viewpoint, but the fact remains that he fails to truly pursue the statements of the New Testament. In other words, he begins with the assumption that the N.T. is erroneous; when he then discovers statements that initially appear to be irreconcilable, he stops. That is, he fails to pursue the statements to see if what appears to be a conflict may, in fact, resolve upon closer inspection. Of course, this is not a fault unique to him. Many people in the liberal end of Christendom do the same exact thing. They come to an apparent problem in the text(s), throw up their hands, and say, "Well, we didn't expect the N.T. to be accurate, anyway, because __________ <fill in that individual's particular rationale>. This is just another example." And then they stop. Meanwhile, those of us who maintain an expectation of accuracy within the N.T. can proceed to dig into the passage(s) and see what possible explanations exist. [Nor is this unique to the N.T. Consider for example the list of kings of Judah and Israel, found in the Hebrew Scriptures (Old Testament). The dates of this list appeared to be irreconcilable for centuries -- indeed, for millennia. But once someone (who we can probably assume held out hope for the O.T.'s accuracy) hit upon the correct ideas for how exactly to measure the date ranges, then it wasn't long before the details were worked out quite satisfactorily.]
And here is a final observation on Rabbi Singer's criticisms of the New Testament
and of Christianity. He argues strenuously that the New Testament (or at least
the Gospels) vilifies all Jews in the worst light possible. Well, that is one
interpretation, I suppose. However, it is certainly not the only one! And while
Singer decries -- quite reasonably and with good cause -- how the Church* has
persecuted Jewish people over the centuries, he simultaneously adopts the same
(warped and inaccurate) interpretation as those misguided elements of Christendom!
To put it another way: there are (at least) two qualitatively different views
of the Jewish people, within Christendom. One view, admittedly, lends itself
to persecution of the Jews. But the other view understands that the Jewish people
are Jesus' people; are God's chosen people; are still beloved by God. It is
mystifying why Singer then aligns himself with the former interpretation
and not the latter! Apparently, Singer fails to recognize the existence
of another (and I dare say, a much more accurate) interpretation of the N.T.
Meanwhile, it is also worth pointing out that the Hebrew Scriptures (i.e., the Old Testament) frequently paint the Jewish people in exactly the same light as do the Gospels. Read almost any of the O.T. prophets -- try a short one, like Amos or Micah, if you like. In the Prophets, we repeatedly read how horrible the nation of Israel is -- its leaders are corrupt, its people do likewise. But of course, the conclusion is not that the prophet hates Jewish people! (Indeed, all the authors are themselves Jewish.) Rather, we must take those statements in the whole context of the book (and for that matter, of the whole Bible). Yes, the people are bad and yes there is judgment coming, but there is hope; God still loves them, there is a remnant, and there is a future. Now... when we read the exact same things in the Gospels, why should we suddenly change our methodology? When there are condemnations of "the Jews" in the Gospels, we must consider the context! The authors (who are again all Jews, with the sole exception of Luke, in Luke-Acts) are doing the exact same thing as the O.T. prophets, at least insofar as this topic goes. The Jewish leaders are bad, and some of the people do likewise -- but there is hope; God still loves them, there is a remnant, and there is a future, and indeed anyone is invited into that future immediately. To interpret this message as anti-semitic is foolish.
Well, there are my thoughts after a first, admittedly brief reading of Rabbi Singer's websites.
(* There are also the questions of [a] whether or not these persecutors are really Christians -- which brings up the question of what is a real Christian, anyway? -- and [b] what ulterior motivations were at work in a given setting -- e.g., political or economic gains may have been rather more dominant motivations than anything religious, in some European strictures/persecutions. But these are not my point, right now.)