That has got to be one of the stupidest things the Watchtower ever printed.
Being limited by the laws of the worldly nation in which we live and also by the laws of God through Jesus Christ, we can take action against apostates only to a certain extent, that is, consistent with both sets of laws. The law of the land and God's law through Christ forbid us to kill apostates, even though they be members of our own flesh-and-blood family relationship.