It’s not necessarily wrong to include violence and the like but there are other times one has to draw a line. It’s not necessarily wrong to discuss about why animal cruelty’s bad, at other times it’s best left to nonfiction (news reports, scientific studies and anecdotes) to do the work. Even a comics writer would realise it in the future.
Violence, like sex, aren’t inherently bad. The real issues are that one has to draw a line and sometimes certain things do have a time and place. You’d be better off understanding animal cruelty through nonfiction reports and studies. It’s not wrong to be curious about those things, it’s just that you have to learn to comparmentalise.
But that’s realising there’s a time and place for those.