Why did Jesus let the demons enter the pigs in Matthew 8?

When Jesus Christ was tempted by Satan, Satan asked him to do certain things which he denied. But in Matthew 8 the demons wanted Jesus to drive them into pigs and he did so. The herd then ran into the water and drowned. Why did Christ deny one request of the enemy but accept another?

In Matthew 8 we read:

Matt. 8:28 When He came to the other side into the country of the Gadarenes, two men who were demon-possessed met Him as they were coming out of the tombs. They were so extremely violent that no one could pass by that way.
Matt. 8:29 And they cried out, saying, “What business do we have with each other, Son of God? Have You come here to torment us before the time?”
Matt. 8:30 Now there was a herd of many swine feeding at a distance from them.
Matt. 8:31 The demons began to entreat Him, saying, “If You are going to cast us out, send us into the herd of swine.”
Matt. 8:32 And He said to them, “Go!” And they came out and went into the swine, and the whole herd rushed down the steep bank into the sea and perished in the waters.
Matt. 8:33 The herdsmen ran away, and went to the city and reported everything, including what had happened to the demoniacs.

The demons in this account occupied the bodies of human beings. The demons made the men extremely violent, so that no one could pass by the tombs. As Jesus approaches the scene, the demons suppose their judgment day has come. Notice that they recognize Jesus is God and their eternal Judge. Secondly, the demons understand that a time of punishment (torment) lies in their future. Thirdly, they seem to know the general timing of their judgment, since they declare Jesus is ahead of schedule.

In reality, Jesus did not come to judge them at that time (see John 3:17), so these demons were not in jeopardy of premature punishment. Nevertheless, they didn’t wait for Jesus to answer their question. Instead, they moved directly to proposing an alternative to the judgment they supposed was coming. The demons proposed to leave the bodies of the men and enter swine instead. It appears they hoped Jesus would accept this “deal” instead of casting them into the abyss. We see this in Luke’s account of the same moment:

Luke 8:26 Then they sailed to the country of the Gerasenes, which is opposite Galilee.
Luke 8:27 And when He came out onto the land, He was met by a man from the city who was possessed with demons; and who had not put on any clothing for a long time, and was not living in a house, but in the tombs.
Luke 8:28 Seeing Jesus, he cried out and fell before Him, and said in a loud voice, “What business do we have with each other, Jesus, Son of the Most High God? I beg You, do not torment me.”
Luke 8:29 For He had commanded the unclean spirit to come out of the man. For it had seized him many times; and he was bound with chains and shackles and kept under guard, and yet he would break his bonds and be driven by the demon into the desert.
Luke 8:30 And Jesus asked him, “What is your name?” And he said, “Legion”; for many demons had entered him.
Luke 8:31 They were imploring Him not to command them to go away into the abyss.
Luke 8:32 Now there was a herd of many swine feeding there on the mountain; and the demons implored Him to permit them to enter the swine. And He gave them permission.
Luke 8:33 And the demons came out of the man and entered the swine; and the herd rushed down the steep bank into the lake and was drowned.
Luke 8:34 When the herdsmen saw what had happened, they ran away and reported it in the city and out in the country.
Luke 8:35 The people went out to see what had happened; and they came to Jesus, and found the man from whom the demons had gone out, sitting down at the feet of Jesus, clothed and in his right mind; and they became frightened.

The demons begged Jesus to accept their proposal, which Jesus did. After receiving permission from Jesus, the demons leave the men and enter the herd of pigs. Upon entering the herd, the demons caused the herd to become crazed and so they ran off a cliff into the Sea of Galilee. Ironically, the demons' desire to avoid eternal punishment resulted in the demise of their earthly hosts.

Jesus had no reason not to accept their proposal, since it served His purposes. First, it resulted in freeing the men from the demons. Secondly, pigs were unclean animals under Jewish law, so they were a perfect symbol and a harmless destination for unclean spirits (i.e., demons). Thirdly, accepting their proposal didn’t change the demons' eternal fate on Judgment Day. Therefore, Jesus accepted their proposal, since the demons were essentially doing Jesus’ work for Him.

More importantly, Jesus was not sinning in accepting the demons’ proposal. On the other hand, Jesus’ confrontation with Satan in the wilderness was quite different. Satan made specific demands of Christ, which were intended by Satan to lead Jesus into disobedience, had Jesus complied.

Therefore, Jesus rebuked Satan with scripture and did not agree to Satan’s demands. This is the key difference between the two moments. The demon’s request in Matthew 8 did not lead Jesus to sin, while Satan’s demands of Jesus were intended to bring Jesus into sin.