  A population of more than 50 binary black hole mergers has now been observed
by the LIGO and Virgo gravitational-wave observatories. While neutron stars are
known to have large velocities associated with impulsive kicks imparted to them
at birth in supernovae, whether black holes receive similar kicks, and of what
magnitude, remains an open question. Recently, Callister et al. (2021) analysed
the binary black hole population under the hypothesis that they were all formed
through isolated binary evolution and claimed that large black hole kicks
(greater than 260 km/s at 99% confidence) were required for the spin
distribution of merging binary black holes to match observations. Here we
highlight that a key assumption made by Callister et al. (2021) -- that all
secondary black holes can be tidally spun up -- is not motivated by physical
models, and may lead to a bias in their estimate of the magnitudes of black
hole kicks. We make only minor changes to the Callister et al. (2021) model,
accounting for a population of wider merging binaries where tidal
synchronisation is ineffective. We show that this naturally produces a bimodal
spin distribution for secondary black holes, and that the spin-orbit
misalignments observed in the binary black hole population can be explained by
more typical black hole kicks of order 100 km/s, consistent with kicks inferred
from Galactic X-ray binaries containing black holes. We conclude that the
majority of the binary black hole population is consistent with forming through
isolated binary evolution.
