Have you ever actually read that study? It has some interesting tidbits in it. For example it found black officers were far more violent than white officers as well as female officers being more violent than males.
Based on the conclusion from that study we should be a limiting minority officers in favor of white male officers.
There's also some interesting flaws with their study. For example it doesn't count who in the relationship was the abuser. So if a cop gets home and his wife yells at him they would be considered part of the 40% because the study counted yelling as domestic violence, as well as not carrying who in the household was the perpetrator of the violence so if it was the cop, the wife, or one of the kids it was all the same.
Then those researchers were never able to imitate their results, nor or any other studies able to get similar results.
other studies have shown that the rate of violence is 7 to 13% among cops while the rate of violence among the general public is 10 to 25%. so statistically speaking cops are far less likely to become violent than the average person, such as yourself.
You can read the study/survey here: Johnson, L.B. (1991). On the front lines: Police stress and family well-being.