GNU comments the BSD-2-clause license in: https://www.gnu.org/licenses/license-list.en.html#FreeBSD, referencing the comments on the BSD-3-clause license as all applying to the BSD-2-clause license.
They specifically state that the BSD licenses are prone to patent treachery.
I find the zlib/libpng license very similar to the BSD licenses. However, GNU doesn't claim the zlib to be prone to patent treachery. Do you know why?