“How can Satan cast out Satan?” (Mark 3:23).
Some rabbis contend that “the slanderer” or “the satan” (as he is often referred to in Old Testament scripture) is just the personification of evil, or the evil thoughts of our own hearts. Some allege that he is a fallen angel, and that seems likely. Others say he’s simply mythical, like Zeus – just a cartoon character with horns and a pitchfork people like to dress up as and laugh about at this time of year.
But Jesus said Satan was a real entity, and had real power in the human realm. Consequently, it would be logical suicide to acknowledge the existence of Jesus and not the existence of Satan.
Perhaps a greater point would be that, frankly, if there is no devil, Jesus was likely schizophrenic. Jesus believed he was engaged in a battle with Satan (Matthew 3:23-27). Jesus believed that he heard the voice of Satan, tempting him, and responded (Luke 4:1-13). Jesus believed that Satan attempted to interfere with the progress of God’s plans (Matthew 13:39; Luke 8:12). Jesus believed that Satan was ruling like a prince over this earthly realm, and that a great part of his earthly mission was to overthrow Satan (Luke 10:18; John 12:31).
Or, the alternative is that Jesus was completely sane, and Satan was and is real, and was and is very much alive (1 Peter 5:8). Take your pick.
If you think Satan is a laughing matter, then unfortunately, the joke is on you.