That depends on whether you believe that the BSD license gives you an implied patent grant - it does, after all, just say "Redistribution and use...are permitted," without saying anything specific to copyright.
See also http://en.swpat.org/wiki/Implicit_patent_licence
If the concept of an implicit patent license is coherent and legally meaningful (it sounds like it is), then an explicit patent license, like Facebook's, would supersede it - and so losing your rights under the explicit license would leave you worse off than relying on the implicit one.
In any case, this is why people like the Apache license and the GPLv3, so you don't have to think about whether a patent license is implied. Both of those have explicit patent licenses with significantly less draconian termination clauses than Facebook's.
(Obviously I am not a lawyer, otherwise I'd know better than to comment on HN about unclear areas of IP law.)
