Of course it's absurd, but that's the argument against traffic cameras which are used to issue citations. If there isn't a cop to chase the offender down and issue a ticket, and there is no accident, it's a true NHNF situation. Those opposed to traffic cameras want to be able to get away with endangering the public, as long as they don't hit someone.
Traffic cameras are another matter.
The normal situation is that traffic cameras don't produce enough
legitimate tickets to pay for themselves. Thus they are basically always configured in an abusive way that racks up the tickets without producing any safety benefit.
Don't be silly. If a traffic camera is issuing tickets to people who have not broken any rules, then that is truly scandalous; but (in all but a handful of cases of embarrassing errors) they don't - they issue tickets to people who HAVE broken the rules - so the tickets they issue are legitimate BY DEFINITION.
Safety benefits are not part of legitimacy; It is irrelevant to the law what speed I can safely drive on a particular stretch of road - the law only cares about what the speed limit is. If I drive at or below that speed, I cannot be penalised for speeding. Safety may be a rationalisation used by the authorities; but it isn't a legal consideration, largely because it is unmeasurable - the cops (or cameras) can measure your speed, but there is no objective measure of your safety.
Configuring a speed (or red light) camera such that it maximises revenue, without regard for any safety benefit, is completely legitimate. Whether it is moral is open to discussion (and given that speed limits are adequately signposted, and that traffic lights are adequately visible to drivers, I would argue that they are indeed moral); but their legitimacy is not in question.
When it comes to road traffic, the objective of the police is to cause citizens to obey the law. Safety may be a result of this; but designing laws to achieve specific goals (be they safety, revenue collection, obedience, or something else) is the job of the legislature, not the enforcement branch.
If safety is the objective, then stopping and ticketing motorists who break the law is far better than camera enforcement; A driver who doesn't even know he is speeding until he gets a ticket in the mail three weeks after the event isn't going to change his behaviour. It is a basic part of human psychology that punishment must be timely in order to deter future transgression, and that delayed punishment is (at best) completely useless.
That doesn't render traffic cameras an illegitimate means to raise funds - indeed, as the tax is purely voluntary, it is a means of funding the government that libertarians should welcome.