I used to consider myself a fan of all things kettlebell related but this is a bit silly. Just because a movement is difficult does not mean it is functional. I can think of dozens of other and safer ways to get a core workout with kettlebells.
Know ye not that your body is the temple of the Holy Ghost which is in you, which ye have of God, and ye are not your own? For ye are bought with a price: therefore glorify God in your body, and in your spirit, which are God's. 1 Corinthians 6:19-20
I beseech you therefore,brethren, by the mercies of God, that ye present your bodies a living sacrifice, holy, acceptable unto God, which is your reasonable service. Romans 12:1