I take it in many cases, if DOO is introduced, it will just be used to downgrade the guard's job to being a ticket collector which therefore would reduce their pay?
Basically, yeah.
As things stand you need someone to drive the train (driverless trains may work on the DLR, but I can't see them on "Network Rail" lines any time soon), you need someone to check tickets and you need one of those two to deal with opening the doors/ train safety etc.
The question is who should do those "extra" bits.
With advances in technology its a lot easier for the driver to operate the doors - should we use improved technology to save money? It's a tricky thing to debate, because it's people's jobs.
DOO clearly works okay - I'm not aware of any "incidents" with it that wouldn't have happened otherwise - but despite the improvements in what *can* work, we've seen the big growth of DOO under BR replaced by a trickle since privatisation (really just a few small sections, like Bathgate to Edinburgh, not the big areas that BR did) - presumably because no TOC has the will for a fight with the Unions. As I've said before, Privatisation has been brilliant for the Unions because its much easier to hold private companies over a barrel (faced with a drop in their revenue) than it is to hold a nationalised company over a barrel (because BR had no incentive to "surrender").
Impossible to debate without certain trolls getting involved though!