Even if cycle helmets don't provide any protection (which I find very hard to believe, possibly that they don't provide much protection, especially if not written properly) then if nothing else they stop your head from making direct contact with the road, which if nothing else would stop a few grazes.
Yes there are times cyclists are idiots (not having lights, not following the rules, etc.) however so are other road users (using mobile phones, not following the rules, thinking that speed cameras are there to steal their hard earned money*, etc.) that are no better. That's not too excuse those cyclists, but rather to point out that other people don't always use the roads as safely as they should and often those that think that they are doing so are the worst offenders.
If there is a problem with lots of cyclists in an area not using lights maybe film it and show it to your local police officer and ask if something can be done. If they can see that there is a clear problem then they may allocate some resources to it. As a few officers for an hour on a few nights, the first to warn and then a few more times over the next few weeks to issue fines and it will be much better. As even those who avoid being caught are likely to hear about it.
(* not wanting to take this thread off topic, but it is easy to ensure that speed cameras don't take your money and that is by obsessing the LAW and not existing the speed limit, it is not the recommended speed but the upper limit. It's also worth remembering that the fines from speed cameras are fairly small, other than the points it is on a par with the fine for shop lifting. A car doing 40 in a 30 is still traveling at well above running pace in the disgrace that a car doing 30 has stopped. Given how much it hurts when you walk into aiming solid running into it will hurt a lot more. Even if it doesn't really in a car/squishy accident it could save you from hitting another vehicle, which if it is bigger than you will cause more damage to your car. Just the inconvenience of having to go through getting your car fixed should be enough to deter people from wanting to risk that too much. Yes there are some speed limits which are difficult to keep below and some which are frustrating, but the vast majority are fine).