Most teachers and administrators think they are fair, but from the child’s point of view, it’s a very one-sided situation.
I guess that the next stage of the discussion would involve assertions that the arbitrary and unfair nature was of particular concern with corporal punishment, rather than with any other type of punishment, for two distinct (and not mutually exclusive) reasons. The first would be that CP can cause long-term damage; others might argue that other punishments such as exclusion from school can also cause long-term damage, albeit of a different kind. The other is that possible sexual aspects might exacerbate the likelihood of arbitrary and unfair use of CP: this is the paraphilia referred to above, though in the context of teachers rather than posters on a forum.