Here is an equation for you: Rain + low light = Poor visibility.
It seems like a lot of drivers don't know their basic math.
If you drive in the rain when it's dark with your headlights off then you are either lacking brain functionality or you are malicious verging on evil. You are an accident waiting to happen and the sad thing is that someone innocent is going to be involved in the accident with you.
I am not saying that 50 percent of drivers drive without their headlights when they should use them and I am not saying that 10 percent of people do this, but if it is 1 percent or less doesn't make it any less heinous or dangerous.
Get a conscience and turn on your headlights. It's against the law to drive in the dark without headlights on and in many states it's against the law to drive without headlights in the rain. These laws are there for a reason and if you have a driver's license you should know the law. It's a matter of safety and thinking about your fellow travelers on the road. It's also a matter of how drivers with mild visual impairments may not be able to see you or young/newbie drivers who may not know to look for dark vehicles.
I don't know if police are concerned with giving tickets for this infraction, but since it is such a dangerous offense I hope that they do, and I hope the ticket is expensive and comes with 4 points (and a dope slap).