In order to work out how dangerous flying at night is, we need to look at the statistics. Perceived risk and actual risk are often very different.
The only fatal crash at night that I can recall was a CFIT crash. I can't recall any fatal crashes caused by engine failures at night in the UK. I would be surprised if night flying weren't more dangerous than day flying, but it may well be that the danger comes from an increased probability of CFIT and loss of control. The single-engine failure that people get worried about may not be much of a factor.