Well done on completely missing the point i'm making. If you'd bothered to click on the article I linked to you'd realise it's a theory that turns the situation on its head and places you in control.
The "let them" theory is nothing new; essentially it's the principle of stoicism which has been around for hundreds of years. What it boils down to is that you are not responsible for the behaviour of others but you are in control of how you react to it. So if someone on your train is playing loud music or having a very loud conversation you have a choice. You can either get wound up by it or you can choose to not let it bother you. I've been practicing the latter option over the past week or so and have found it surprisingly liberating!
It can work for some things (such as crying children or people having phone calls, which, let's face it, are going to happen in any public place) but on a wider social level it just encouraged anti-social behaviour. There's a line that can be drawn -- one should not be as prickly as the guy in the Torygraph article, but on the other hand if you just let some actual problems go, you end up with a free-for-all that suits no-one. The idea legitimises selfishness and the idea that your needs for audible entertainment trump everyone else's.
There was a really good transport campaign a few years ago, roundabout the beginning of the pandemic, which encouraged people to be considerate towards disabled travellers and to recognise that even if people don't look disabled, many of us are. (I made my own situation better by breaking my ankle and having to use a walking stick, so I do now 'look' disabled, but I've always been autistic and jumped on the sunflower lanyards when they became a thing.) They still exist in some parts of the transport network but not to the same degree as in early 2020. But that kind of campaign educated people as to the struggles some people face when travelling and asked them to look out for people who may not necessarily look like they need help but actually need a little bit of space to navigate things. SWR (and I've heard other companies do this too) offer badges that ask people to offer a seat to the person wearing one.
While, yes, you can't control other people's behaviour, that doesn't mean we should just tolerate everything. It would mean we couldn't ask people not to litter or smoke in public places or offer their seat to those who need it (I should just be stoic and stand even though it causes me actual pain for most of my journey? It almost happened once -- I got a stink-eye from someone I asked to move from a jump-seat once but she moved). The topic of the thread isn't crying babies or people having phone calls at a reasonable volume -- it's people actively doing the audible equivalent of littering.
And I think the transport companies have a definite right to try to change that behaviour back to how people behaved before the pandemic.