It sounds like he may have had some experience with the Church, enough to develop a grievance with our standards of living. For example, we follow a health code called the Word of Wisdom, which teaches that our bodies are temples. Because of that, we avoid alcohol, tobacco, coffee, tea, and recreational drugs, and we’re encouraged to show respect for our bodies—including being cautious about tattoos or excessive piercings.
That being said, I’ve personally attended an LDS temple and seen a member with tattoos officiating a temple ordinance. I actually thought it was really neat—it reminded me that we’re all imperfect people just trying to live our best lives. I’ve never heard of anyone being told they must remove tattoos to be considered worthy for the temple. In my experience, it always comes down to a person’s current choices and how sincerely they are striving to live the teachings of the Church.
Of course, I can’t speak to this man’s personal experiences with members of the LDS church. Maybe someone said something that offended him. But whatever the case, it certainly doesn’t justify violence of this nature.