That's not entirely true.
Both "Judaism" and "Christianity" of the time were typified by extreme religious diversity. Some groups were tolerant of others and some groups weren't. This is actually keeping in line with the Hellenistic culture of the time as a whole, in which religious diversity was openly embraced and pervasive (as opposed to the elitist slaughterings that were initiated upon the establishment of "Christianity" as the state religion).
Contrary to what many "Jews" and "Christians" have been handed down, neither of these religions were particularly uniform or homogenized during the 1st and 2nd centuries. In fact, they were probably far more diverse and variegated than they are now (a fact that many so-called "true believers" find infuriating).
You can even see this in the New Testament itself. The writer "Paul" has very different takes depending on which of "his" letters you're looking at (the overtly Gnostic tendencies of Galatians contrast greatly with the fundamentalist/literalist rantings of the Pastorals). This was because the Pauline letters, attributed to a single man, were actually written by various different individuals --- obviously proponents of different schools of "Christianity". The same could probably be said for the Synoptics themselves, as well.
"Christianity", by its very nature, is an inherently diverse and variegated religion, with very different views and schools of thoughts on things. I could find parts in the New Testament that support free will and parts that support fatalism. I could find parts/passages that support relativism (particularly in Paul), and parts that support the moral absolutism of the fundamentalists. I could fine parts that support monotheism, and parts that support a Buddhist-style monism or pantheism. I could find parts that support the trinity, and parts that do not.
Think about it.