Marcion of Sinope
The reason for this argument is a disagreement about the proper interpretation of the word "fulfillment" (πληρῶσαι; plerosai). This goes back at least as far as Marcion of Sinope and continues until today. Many modern scholars now consider these four verses to be a prelude to the Antitheses, but this position is not universally accepted, and many continue to interpret Matthew 5:17–20 independent of its textual neighbors.