Repentance
Over 370 religious leaders from across the world signed a declaration asking for forgiveness for harm caused to the LGBTQIA+ community, but the Church doesn’t practice what it preaches. It doesn’t say “sorry.”
It is credible, therefore, to infer that the “these things” he was referring to are in fact any activities that lead to others’ loss of faith. Alma would have his son and anyone within the sound of his voice understand that spiritual injury to others is comparable to physical violence.