  We report a mechanism capable of reducing (or increasing) stellar activity in
binary stars, thereby potentially enhancing (or destroying) circumbinary
habitability. In single stars, stellar aggression towards planetary atmospheres
causes mass-loss, which is especially detrimental for late-type stars, because
habitable zones are very close and activity is long lasting. In binaries, tidal
rotational breaking reduces magnetic activity, thus reducing harmful levels of
XUV radiation and stellar mass-loss that are able to erode planetary
atmospheres. We study this mechanism for all confirmed circumbinary (p-type)
planets. We find that main sequence twins provide minimal flux variation and in
some cases improved environments, if the stars rotationally synchronize within
the first Gyr. Solar-like twins, like Kepler 34 and Kepler 35, provide low
habitable zone XUV fluxes and stellar wind pressures. These wide, moist,
habitable zones may potentially support multiple habitable planets. Solar-type
stars with lower mass companions, like Kepler 47, allow for protected planets
over a wide range of secondary masses and binary periods. Kepler 38 and related
binaries are marginal cases. Kepler 64 and analogues have dramatically reduced
stellar aggression due to synchronization of the primary, but are limited by
the short lifetime. Kepler 16 appears to be inhospitable to planets due to
extreme XUV flux. These results have important implications for estimates of
the number of stellar systems containing habitable planets in the Galaxy and
allow for the selection of binaries suitable for follow-up searches for
habitable planets.
