Nigel - what is the safety procedure the company is trying to remove?
Short answer - the safety responsibilities of the train Guard.
I try to provide just the facts that affect tourists, without getting into the to and fro that such disputes bring, but I have been asked a direct question and would like to elaborate on an answer previously given by another.
A Driver is responsible for moving the train safely from A to B. They need all their concentration to do that.
A Guard is responsible for the safety of the passengers (and other staff) on board a train.
That includes dealing with ill, vulnerable, sleeping and unruly passengers (hopefully not all at once) and looking out for the welfare of all.
The most dangerous place for passengers is what is called the Platform Train Interface - the PTI. It is that bit of the world between the edge of the platform, and just behind, the gap between (with the change in height) and through the doors into the train.
The Guard is uniquely able to position herself or himself where they can see the entire length of the train - as many as 12 cars - and the approaches to it, and can see that the entire train is safely accommodated in the platform (yes, sometimes drivers make mistakes and door could be released from which passengers could and have stepped out into thin air) and that before closing the doors all passengers are clear of the PTI and the train can be dispatched safely.
In case of an accident the Guard is responsible for the passengers and the Driver the train, but if the Driver is incapacitated or unable the Guard is fully trained in the technical requirements of protecting the train.
In my many years on the railway I have seen people fall down the gap of the PTI and had their lives saved by the prompt action of Guards, drunks leaning on the train as it started to move, and drunks and vandals attacking the train before it moved, and vandals setting fires, attacking passengers, urinating on the seats, and much more - all invisible to a Driver - but where Guards have stepped in and saved lives and property.
Station calls are much more difficult on curved platforms and at night in the rain.
That is just a few of the safety duties of a Guard, and there are commercial and revenue protection duties too.
What Southern want to do (and Great Western Railway right after them if they succeed) is remove the safety responsibilities (and training) of their Guards and reduce them to solely revenue focussed.
It is much more than pressing a button.
Which of those duties would you, as a travelling passenger, like to do without?