If you asked St. Augustine why he believed in an immortal soul, I suspect he'd look at you quizzically, raise an eyebrow, and utter a dismissive, "Because St. Paul did!"
If you ask Pete Rollins why he thinks belief and unbelief are compatible--and even desirable--states for the Christian, he's got his answer ready to go: "Because Jesus said so on the cross."
Of course, there's large groups of Christians who might accept the rationale for Augustine's answer while simultaneously deploring it. After all, we now know that it was that blasted Hellenstic influence and its pesky dualism. It's almost like magic: wave a hand, utter the magic words, and the problem goes away.
Or better, it's like a trump card. The syncretism card. Play it, and you immediately put your theological opponent in a place where they have to justify not only their interpretations of Scripture, but have to demonstrate that those interpretations haven't been unduly tainted by the (obviously) problematic philosophy in question.
It's a little more combative, a touch more polemical than the mystery card. But it's still effective when you're in a tough theological conversation and you're not sure how to escape unscathed. By which I mean, "admitting you might be wrong."
It's best if this card is played deftly. Rather than shouting, "syncretism!" speak softly about the "[insert nefarious philosophy] influences" on their position. That helps you avoid having to say precisely what those influences are, or how they got to be there.
(Just beware the counter card, the "baptized!" rebuttal. This is played by those who shamefully attempt to sanctify their use of obviously wrong categories to interpret Scripture by drawing an analogy to baptism.)
This "syncretism card" is a game we can all play. Here are some common (though not necessarily ones that I endorse!) accusations about the nefarious thinkers or movements that certain streams of Christianity have gotten in bed with. And if I missed any, feel free to add them in the comments.
There are plenty others out there. And there's a serious point (and question!) buried here about the shape theology takes, and how well it fits with competing anthropologies.
But mostly, it's just fun and reminds us that the "syncretism" card can be turned against us pretty easily. Make sure to deploy it with care.