Just because a cyclist rides up the side of a lorry doesn't make them stupid, it makes them inexperienced. everyone makes mistakes, and more so are made in this scenario because there is often a nicely painted cycle lane inviting the inexperienced cyclist into it. Often young people (and particularly girls i think) and those that don't drive do not understand the turning circle of large vehicles. And having done it once, and nothing untoward happens, they continue to do it blissfully unaware of the danger. No one goes out the house in the morning to die and no one goes out the house meaning to kill. But the responsibility is always on any driver to take more care around road users more vulnerable than themselves, whether that be a car driver or lorry driver. Inexperienced cyclists do not deserve to die because they chose, legally, to ride up the inside of a lorry and the driver, for whatever reason, does not see them (be it his mistake or not) and neither should the driver have to suffer the trauma, which is why everything should be done to reduce these terrible accidents. If that means debating whether to install camera's, sensors or audible alarms whilst taking into account all angles/circumstances, then so be it.
The bottom line is, it's not illegal to either filter or wear headphones, and although opinions will always vary, just as with helmets, the fact remains that this scenario exists and therefore should be considered when debating what equipment to install. And if a company install a £600 system that fails because the cyclist doesn't hear it then it is, literally, a waste of money. I do think however, as stated earlier by another poster, that the alarm is very loud so likely to be heard by someone wearing headphones.
