Western Buddhism is hardly syncretic. First day in my intro class (not led by a western hippy, rather, a Thai monk) said that you are not required to accept everything claimed to be Buddhism in order to be Buddhist.
Having to believe the entirety of a canonical text, I'll leave that schtick to Christians, thanks.
there are modernist trends in buddhism. especially the forms of east asian buddhism that was transmitted to western countries during the 19th and early 20th century century, are derived from modernist buddhisms that sprung up in places like burma, thailand, japan and others.
the japanese zen that came to america from people like d.t. suzuki, were transmitted by people who - from the perspective of japanese zen - were minor, unsuccessful, marginal figures in japan for a variety of reasons, some of which were their views which were unorthodox or unconventional. when they came to america though, they became very successful.
the thai forest tradition, or the burmese popular meditation movement (vipassana) are quite recent inventions and reforms. before recently, the vast majority of buddhists in history never meditated and the idea of meditation was a kind of elite practice practiced by some, not even most monks. this was an asian invention, which has become very popular in western ideas of buddhism, so that most westerners who have heard of buddhism inevitably link it to meditation.
again let me emphasise: there are modernist east asians as well. just because we east asians are east asians doesn't mean we also don't also change our religions. buddhism is like christianity, buddhists are like christians in this regard, because we are humans and we are religious people.
and though
you, a lay househoulder may not have accept everything
claimed to be buddhism, thai monks *do* have to accept the theravada canonical texts, which from a theravada pov, is not just claimed to be the words of the buddha, but actually ARE the words of the buddha.
western buddhism is not necessarily the kind of atheistic buddhism that for some reason many atheists seem to have taken up. the western buddhisms practiced are very diverse indeed and i think you'll find many sanghas in the west are traditional. it's common, i find, for teachers to 'change' or de-emphasise certain aspects of the religion for new converts or listeners. a thai monk may speak differently to a western audience of potential converts than to his native audience back in chiang mai.
Actually it was the Buddha who taught that you shouldn't be required to accept things on authority or just because they are taught to be "Buddhist". Doesn't take syncretism for that idea to appear in Buddhism:
"Do not believe in anything simply because you have heard it. Do not believe in anything simply because it is spoken and rumored by many. Do not believe in anything simply because it is found written in your religious books. Do not believe in anything merely on the authority of your teachers and elders. Do not believe in traditions because they have been handed down for many generations. But after observation and analysis, when you find that anything agrees with reason and is conducive to the good and benefit of one and all, then accept it and live up to it."
- Kalama Sutta
Not that there is anything wrong with syncretism though. It would be silly to close yourself off to theories and ideas just because they happen to come from outside your favorite sect.
that's really the favourite proof text used by a lot of atheist buddhists in order to reject ideas like rebirth, which would be beyond the pale for most of buddhist history (i.e. a heretical idea), but you should be aware of strong objections to what they see as gross misinterpretations of it by people like bikkhu bodhi and thanissaro bikkhu:
http://www.accesstoinsight.org/lib/authors/thanissaro/lostinquotation.html
http://www.accesstoinsight.org/lib/authors/bodhi/bps-essay_09.html