Larry, you rightly point out that the criterion of dissimilarity is a rather odd principle of historiography. I agree with your third point about the seemingly anti-Jewish thrust of the criterion, if I may put words in your mouth. The articulation of the criterion, at least in the 1950s and '60s, was closely related to the investment of Christian theology in "finding" a Jesus who was incommensurable and represented a definitive expression of divine will and purpose. That theological interest had the effect of skewing badly the already problematic criterion, leading to some rather wild mischaracterizations of Second Temple Judaism and rather dazzling efforts to turn Jesus into someone who transcended his historical environment completely. This is not history, but apologetics.
You're also right to distinguish the so-called criterion of embarrassment from the criterion of dissimilarity and to favor the former over the latter. Yet, the criterion of embarrassment yields little data and has some of the same methodological problems as its counterpart—namely, it presumes that the things Jesus is best-known for, and which most characterized his activities, were things that his followers were embarrassed about. I have no quarrel with your two candidates—the baptism of Jesus by John and the fact of Jesus' ignominious death at the hands of the Romans. It does appear that the Jesus movement was embarrassed about these two events. It's clear that the evangelists took steps to explain why the baptism took place. And both the evangelists and writers like Paul tried to get around the shame and humiliation of the crucifixion. Luke, for example, stresses that Pilate believed Jesus to be innocent of any charges brought against him but acceded to the demands of the priests. Matthew has Pilate's wife receive a dream, as a communication from God, indicating that Jesus is a righteous person. Paul understands Jesus' death as a divinely wrought event that effects salvation for humankind.
But I wonder whether your privileging of these two data also tacitly assumes that it was the really embarrassing things about Jesus that most essentially characterized him. The two are not the same. Surely it is likely that at least some of his followers weren't embarrassed at all about other activities that were characteristic of Jesus. For example, a critique of wealth and status is quite widespread in the Jesus tradition (e.g., the sayings in Gospel Q; Matthew, Mark, and Luke; the Gospels of Thomas and James). This of course doesn't distinguish Jesus from certain strains in Second Temple Judaism: The letter of Enoch, for example—a Jewish composition from about 170 B.C. attributed to the Enoch mentioned in Genesis 6—is very hostile to the wealthy. But it's also clear that Jesus' followers—at least some of them—took up this critique of wealth without any embarrassment; in fact they defended and elaborated upon it.
My point here is that we must also guard against identifying what we can most securely attribute to the historical Jesus with what was most characteristic for him and for the Jesus movement. For this reason, I think that the criterion of multiple attestation—which looks for motifs, sayings, and stories which appear in many independent streams of tradition—has some advantages. This criterion, not dissimilarity, by the way, is at the heart of the method of the noted commentator John Dominic Crossan.
Coming to your own two examples: Jesus' baptism by John is surely a relatively secure historical datum of the Jesus tradition. But almost everyone who comments on it—E.P. Sanders and Crossan, to take two very different approaches—agrees that Jesus was also distinguished from John in significant ways. Sanders argues that Jesus did not insist on repentance as a precondition to embracing the kingdom. John did, as did most others. Crossan says that Jesus began as a disciple of John but eventually abandoned John's futuristic eschatology. We could both pile up examples of good scholars who acknowledge the connection between John and Jesus but who also insist that ultimately they were up to something quite different. You conclude, quite reasonably of course, that Jesus' association with John suggests that "Jesus shared John's urgent concern about the religious state of his people"—I'd say it was more than just religious—and also shared "John's firm confidence that the time had come when God was about to set in motion some decisive events that would bring about God's kingdom." Sure. But there are some pretty clear differences between what John seems to have in mind and what Jesus thought. So, in the end, this unassailable historical datum turns out not to be quite as telling as we might want. It's a bit like Socrates and Plato. Socrates was Plato's teacher and no doubt a formative influence on him. But Plato went intellectually to places that Socrates did not, and we can't be very sure of how much Plato's Socrates represents the historical man.
The issue of the causa of the crucifixion is also a problem. Jesus was crucified, and perhaps Pilate had a titulus (inscription) affixed to the cross suggesting ironically that here lay a messianic king. The real gaps lie, however, among what Jesus might have thought he was about, what enthusiastic followers and other observers might have thought he was about, and what Pilate or his informants thought. I'm reminded of Pliny the Younger's remarks to the emperor Trajan in about A.D. 114. Pliny reports that he has not found anything especially dangerous or pernicious about two Christian deaconesses he has examined—apart from their "excessive superstition." But he has decided to execute them anyway—probably on the grounds of their resistance (contumacia) to a magistrate. We just don't know what Pilate thought of Jesus, if he bothered to think much at all, because the evangelists have so overlaid the report of the trial with apologetic elements.
So, I'd agree that Jesus was baptized and crucified. But these data don't tell us all that much.