The best income will, I'm sure you will appreciate, also include value for money for tax- and farepayers, however. If too many people are priced off trains into cars, the transport system as a whole is less safe.
That is not unsafe because it is DOO, but because someone didn't do their job properly and check that the train was clear before departing. There was, after all, that incident where someone fell down the side of a Merseyrail train and was killed, and that occurred because a guard belled the train off with someone leaning on it. Not really any different.
*If* it is established that the incident occurred because the driver could not see the passenger trapped in the doors (perhaps because the monitors/mirrors did not give an adequate view), then that's perhaps one for the anti-DOO argument. But if it is established that the driver could see, but didn't check, then it isn't, as a guard could easily have made the same error.
You *could* feasibly come up with a safer system where guard operation was used as at present, but the driver additionally had mirrors/monitors and made an additional check. But that is not how guard operation works in the UK. If the driver receives two buzzes/bells, they don't have to check further that those signals were not in error, at least in terms of passengers stuck in doors.