To successfully rebut this claim you need to understand why drivers indicate in the first place, and what the purpose of any indication is.
According to Rule 103 of the Highway Code "signals warn and inform other road users, including pedestrians, of your intended actions." It goes on to suggest that signals need to be given in plenty of time, be used advisedly so that they do not cause confusion and always be cancelled after use. It is important to remember that signals do not give you the right of way and, just because you have signalled, you should not assume that others have seen or understood it.
So, to extend Berkeley's philosophical question of "if a tree falls in a forest, and no-one is around to hear it, does it make a sound", if a car indicates at a junction and no-one is around to see it, has it actually informed anyone? If we conclude that it hasn't, then the next logical question is why did the driver feel the need to indicate?
The answer to the above is probably either because it is a habit and therefore an automatic reaction, or because there may be someone who the driver has not yet seen and "it is better to be safe than sorry". Neither of these answers are satisfactory.
Drivers who drive by habit are not generally thinking drivers. They are drivers who drive the same route each day, at the same time and encounter the same hazards. They are the drivers who write "suddenly ... appeared" on their insurance claims when what they actually mean is "I didn't see it because I wasn't expecting it". In short, they are dangerous drivers. Only by thinking and using our powers of observation can we accurately assess the conditions in which we drive. Whilst we may drive the same route each day at the same time, it will never be the same journey, since a number of variable factors (weather, road conditions, state of mind etc) come in to play each time we get behind the wheel. We therefore have to be constantly alert.
Equally, indicating "just in case", also demonstrates that we're not alert. Drivers have to assess and reassess the information that they have around them. It may change forcing driving plans to change to reflect this. Doing something "just in case" shows that the analysis needed to be an advanced driver is not yet present.
The correct method is therefore, during the information phase of the System, to make a judgement as to whether there is anyone around who will benefit from your signal. The information phase encircles all the other phases, which means this is constantly reassessed and the course of action changed depending on circumstance. If there is no one to benefit then no signal need be given. However, if someone does appear at any point whilst negotiating the hazard, then a signal should be applied.
By doing this you are demonstrating that you're a thinking driver, helping to reduce the clutter of unnecessary signals and cutting down on the number of hand movements you need to make. All of this will make you a safer, better driver.
The correct statement should therefore be "Advanced Drivers Don't Indicate Unless They Have To".