Both the statement reportedly made by Jesus (“Whoever is not on my side is against me” & “He that is not against us is for us”) may not have been made by him because both the statements lack meaning. For example, many of the divorced couples are not on each other’s side, and are neither against one another nor supportive to each other.
In view of the other statements Jesus made, the statements he could have made could be something like this:
‘Whoever is not on my side is not against me but is great as he is neutral;
He that is not against us is not for us but is great as he is neutral.
Jesus taught neutrality through his action when he said: “Give to Caesar what is Caesar's, and to God what is God's” (Mark 12:17; Mathew 7:12, 21-23)