In Mark 3:21, Jesus’ family thinks he’s mentally ill. They come to take custody of him, which is the right thing for your family to do if you’re mentally ill.
In Mark 3:22, some of the scribes think Jesus is demon-possessed, and they let everybody know it: “He is possessed by Beelzebul, and by the prince of demons he casts out the demons.”
That Mark places these two reactions together is no accident. His gospel is brief and highly selective; he’s not trying to write an exhaustive account. What’s his point?
Whether you reject Jesus with sympathy (perhaps as a good moral teacher who was tragically misunderstood) or with anger (perhaps as a demon or an outright fabrication) doesn’t matter. What matters is whether you accept him or reject him. As Doug Wilson puts it, “We don’t get to pat Jesus on the head.”