It's been a problem in the NFL for a long time. The art or sport imitates life. Really though, it's a society issue, because these players don't just pop up in the NFL. They come from bad backgrounds and slide through the educational system. The numbers of domestic violence may seem high compared to outside the league, but it's a law of averages.
You have 53 players on 32 teams which adds up to 1,696. Add up to 8 players that can be on each teams practice squad and you end up with over 1,800 players in the NFL. If you have just 3% of those players get into some case of domestic violence, that's 54 players. That may seem like a lot but the total number of players are a small fraction of society. Whatevers the case, these problems are not going away. The league can let the bad players that are convicted of crimes go and these people will be part of regular society. They will not be public figures anymore, will bring their problems and possibly create more crimes.
Really looking at it though, the NFL doesn't guarantee contracts and ANY player can be released at ANY time. It can be for performance or in the current situations, conduct issues. These careers are extremely finite. IMHO, the bad players eventually get weeded out of the league. Their criminal record catches up with them or their team just loses patience with their conduct.