Is some of the disdain for John the Baptist by the Pharisees and religious leaders because of his choice of food as well as preaching?
It was certainly not preferable to eat bugs like locusts but the law did allow it. I think his choice of diet had to do with living in the wilderness. It’s not like he went into town into Jerusalem to buy groceries and only went out into the wilderness to baptize people.
He lived in the wilderness around the Jordan River. People came out to him to be baptized by him. He was a weird creature. His gruff lifestyle would have reminded them of Elijah the prophet. They even asked him if he is Elijah.
Although his diet may have had a little to do with it, the Pharisees and religious leaders disdained John because of a number of his practices. First, he was baptizing people in the middle of nowhere. Baptism was usually reserved for the temple area, and the Pharisees regularly practiced washings for purity. Water baptism occurred for proselytes who converted to Judaism.
But using water baptism to prepare the way for the Messiah and to call people out on their sin issues was not normal. He didn’t follow in the footsteps of his Levitical father who was a priest in the Temple. Instead, he rejected that approach and did his own thing out in the middle of nowhere.
Aside from this, he caused a lot of issues with the Roman-placed leaders of his day. His preaching was not something they could smooth over with the Roman officials. I have to wonder if they asked him if he was the Messiah out of hope or out of consternation that he would cause even more trouble. False messiahs had been rising up in Israel for many years. And they always caused trouble with Rome.
Most of all, I think their disdain for him was the same as it was for Jesus. He became very popular and they wanted to be the popular teachers of Israel. They didn’t want to share the limelight with anyone else whether he was from God or not.
The disdain of the religious leaders for John the Baptist was most likely a combination of all of these factors. John was no friend of anyone in the religious hierarchy of Israel. He preached against them, called them a brood of vipers, and saw them as against the move of the Spirit in bringing Jesus the Messiah to Israel.