I agree the plain BSD 2 and GPL licenses are compatible. The issue here is how the PATENTS file from Facebook reduces an implicit patent grant by the BSD license making BSD+PATENTS into essentially a different license with less permissions than plain BSD.
According to the FAQ on the GPLv3: https://www.gnu.org/licenses/quick-guide-gplv3.html "Whenever someone conveys software covered by GPLv3 that they've written or modified, they must provide every recipient with any patent licenses necessary to exercise the rights that the GPL gives them."
So, since GPLv3 talks about patents, and the Facebook PATENTS clause reduces the implicit patent grant of BSD, I feel it is in scope for GPLv3. A plain BSD 2.0 license with an implicit patent grant would presumably provide enough patent rights to be compatible with GPLv3. To my reading of the situation, BSD+PATENTS does not seem to provide enough patent rights to comply with GPLv3 (because of the one-sided retaliation clause of Facebook's PATENTS file).
The GPLv2 is a different story which is less clear to me.
In section 7 GPLv2 says: "If, as a consequence of a court judgment or allegation of patent infringement or for any other reason (not limited to patent issues), conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this License, they do not excuse you from the conditions of this License. If you cannot distribute so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not distribute the Program at all. For example, if a patent license would not permit royalty-free redistribution of the Program by all those who receive copies directly or indirectly through you, then the only way you could satisfy both it and this License would be to refrain entirely from distribution of the Program."
So, because some of your downstream users might not have a valid patent grant from Facebook if they sue Facebook for infringing their patents, does the last sentence imply you can't distribute the combined BSD+PATENTS and GPLv2 code?
Facebook is offering a separate patent license, and that is out-of-scope of the GPL.