Earlier quoted context omitted.
Not knowing what to believe is probably the best thing right now. Everett (the linguist who made the claims) is quite insistent that this is the case, many other linguists are not. It's definitely a big controversy right now, particularly Everett's claim that Piraha does not allow recursion (many linguistic theories, notably Chomsky's, seem to make recursion a pretty fundamental feature of human language). A lot of t…
When you have one data source and only a handful of data points and that data is not reproducible, you're not doing science. Everett might have some interesting hypotheses, but what he's doing isn't what you could call peer-reviewable. Linguists who have aspirations towards hard science will, for that reason alone (not to mention the theoretically tenuous/unpopular nature of his claims) dismiss him pretty quickly.
Coming up with crazy ideas based on some strange observations is a part of science too.