Let's see if you and I can nail this.

Public transport has an implication that generally people turn up for their transport and buy it. Even so pretty much of all of pre-bookable public transport that includes babies has the booking made for the adults and the baby comes along with the adult without being in anyway having to be pre-declared. Even on premium travel eg First Class rail travel then the most that anyone reasonably expects is the slight possiblitiy of a better chance of a seat and virtually no certainty of calm peace or quiet. No sane person is suggesting for this type of "public transport" should include the restriction on baby travel.

I suggest that First Class and Business Class Air travel is completely different.

Firstly the provider goes to great lengths to differentiate expectations from what should be expected further back. Secondly in improving the chances of providing what's been promised, compared with other forms of transport every passenger INCLUDING BABIES has to be declared in a booking before the booking is accepted by the travel company.

So an option not available to providers of other forms of so-called public transport is available to airlines. To expand - whereas anyone and everyone can get on a bus - absolutely no one can get on a plane without booking. This means that the airlines do have the practical opportunity of deciding who goes on their flights and where they sit and therefore how far they are prepared to go to reasonably underwrite their advertising promises.

In this respect therefore air travel is completely different from public transport generally.