Yes, I have seen this assertion in Protestant circles before. My first thought is, anybody making such an assertion today on such flimsy evidence would certainly be the loser in a libel suit.
Some translations say “family”, others say “friends”. Some say that the family/friends said “he is beside himself” while others say that it was the crowd who said this.
Now, if we allow for argument’s sake that it was family, and the family members said “he is beside himself”, we are still a million miles away from “Mary denied Jesus”. Did all of the family appear simultaneously and cry out in chorus “he is beside himself”? That’s not how groups of people normally act and talk. And why did they say “he is beside himself”? Because they thought he was mad? Or because they were trying to protect him from the great crowd “lest they should crush him” (Mk 3:9)?
And even if “his family” denied him, was Mary there, participating in the denial? Mary, who knew from the beginning that “The Holy Spirit will come upon you, and the power of the Most High will overshadow you; therefore the child to be born will be called holy, the Son of God”? Did she forget how Jesus was conceived? Did she forget the appearance of the angel Gabriel?
And finally, why, if Mary was in the first group, are the two groups described in such different terms? In Mk 3:21 they are called “family” or “friends” or “kinsmen” while 10 lines later in Mk 3:31 they are called “his mother and his brothers”. If these are the same groups of people, why are they described differently less than a dozen lines apart? Why is Mary’s presence explicitly noted in Mk 3:31 but not in Mk 3:21?
The whole Mk 3:21 argument is the flimsiest possible attempt to find fault with Mary and, the real goal, with the Catholic faith.
