At issue is whether psychological aggression -- name-calling, arguing and slamming doors -- and physical abuse between parents leads to harsh parenting in a high-risk sample across the early years of child rearing.
"We have long been aware that high levels of family conflict can have a negative effect on children's development, but most people tend to think that this doesn't apply to babies. In fact, we are now finding that this notion of toxic stress in families applies to babies as well,"...[emphasis mine]
While you may not have a high risk family, it's unlikely that psychological aggression is totally harmless in other families.
To say "Most people tend to think that this doesn't apply to babies" is crazy. It's common sense! I was in an abusive relationship as a teenager and became pregnant. The abuse of course got worse when my son was born. His father and I were together for two years after he was born, so he witnessed more altercations, whether verbal or physical, than I care to admit. Even though I got out of the relationship when he was two and have been in a loving marriage since he was 4, those two years affected the young man he is today.