Socrates is ridiculing
Meletus by having him state before the
jury that Socrates,
alone, corrupts the youth and that all the other Athenians improve them.
(Meletus does not want to offend anybody in the
jury!) Socrates humorously
points out that this is the opposite state of affairs of what one finds in
nature. For example, there are far more people who can ruin the training
of a horse than those (such as a horse trainer) who can improve the horse.