Jesus cast out demons setting people free from spiritual torment. The Pharisees accused him of casting out demons by the power of Satan. Jesus pointed out the illogic of their reasoning. Satan does not cast out his own servants. If he did that he would be thwarting his own plan to destroy people.
The problem for the Pharisees was that if Satan was not casting out his own servants then the only one left to attribute it to would be God. If God was casting out the demons, they had no choice but to recognize Jesus as righteous. If he was a righteous man, then all he said was true and that would leave the Pharisees in a very bad position.
People who do not want to know the truth will avoid it even if it means being illogical. The smartest people can make the most foolish decisions when they are based on emotions and not on the truth (Mathew 12:25-30)
