So we're agreed that your conception of decency isn't 'common'. In which case, why should it be enforced? What privileges your version ahead of another?
I start with the presumption that if people are going to share public space, often at very close quarters, then they need to be considerate of others.
People's preferences and sensitivities vary, ranging on a scale from those that are concerned about nothing except violence directed at them, to those for whom the very presence of others is an irritant to be endured where it cannot be avoided.
Obviously, we cannot please everyone all the time.
However, there is a long-established principle that one should make sacrifices where necessary to contribute to the comfort of others when in public. It is this principle that has disappeared for many people and has led to a range of behaviour, from the minor incivilities to major disorder, that plague our city.
As an example, some people enjoy loud music but most people find it very annoying, especially where it is others' music over which they have no control. So we prohibit music that is played loudly where it annoys others. This is justifiable because we do not want the preferences (it's hardly a necessity) of some to lead to the misery of many. Further, we make no general prohibition against music, or even loud music in contexts where it will not annoy others. This is considered by most people to be an appropriate balance.
I don't think that this measure against drinking on the tube is designed to stand alone. It represents the first of a range of measures to restore this "sacrifice principle" to behaviour in public. Individual instances of drinking on the tube may be perceived as anything between irritating and uncouth, all the way to grossly threatening. Mr Johnson is asking all Londoners to forego the dubious pleasure of drinking on the tube not because it in itself presages the fall of civilisation, but because it's a small way in which the tide can be turned from individual selfishness to a more widespread consideration of others' comfort.
I suspect there's also a "Broken Windows Theory" motivation here, but that's for another post, if not another thread.
