Yes, I was once teenaged, but can't remember riding about without lights
How long ago? Many of us can remember riding home cautiously after our "never ready" lights had packed up yet again, or at least gone so dim that they were almost surely below the minimum 4 candles brightness.
If there was any incident/knock-down/RTC, there could be repercussions, if he tried to claim from the motorists insurance
He'd probably not get a penny, due to the lighting issue (not legal for road use) & could even have an attempt to recoups some costs from him, by the insurers
It shouldn't be zero payout but may be reduced by the motorist arguing that lights sweeping across their face would have triggered them braking sooner and sharper and thereby reduced the severity of the collision. For it to be zero payout, the motorist (or their insurer or lawyer or...) would need to argue successfully that they hit an unlit object in the roadway which they would not have hit if it had been lit - in other words, to argue that they were driving so they could not stop within what they could see to be clear positively - or in short, that they were driving carelessly. I rather hope no court would accept that unless the motorist had been convicted before the civil liabilities trial, but I've not searched the case law.
Does hardly anyone these days stop to think how absurd it is that we demand that all others conform to the whims of motorists and ride with lights, reflectors and reflective gear at night
No, because I want to be seen/get home safely
Why is that an either/or? Can't we want to get home safely AND lament how shoot our road culture has become?
Also, one more thing to think about: ninja cyclists seem to be underrepresented in collision reports. One theory is that they don't make the mistake of assuming that motorists have seen them, unlike hi-vis daffodils.