My instinct would be that the best (and pretty
weak) case for good faith, reasonable proportionality, etc would relate not at all to the group of protestors who were
contained, but either to some
argument relating to the resource pressures of policing adjacent events, fears of the risks of issues involved in one becoming mixed up in the other, etc, etc which (at its very best) would be a highly pre-emptive and precautionary approach to a situation where there was no existing problem to be
contained.