Is there some wonderful reason why the Strathclyde arrangement cannot be applied across the whole country? The driver is entirely responsible for the train and making it move but all services are diagrammed to have a ticket seller on board who would fulfil most of the safety roles of a guard. If the ticket seller person is unavailable the train can still run but it is never planned that way, making services more resilient against staffing problems. The ticket person doesn't have an excuse to hide in the back cab, even if it is busy, because they don't need to get to the door control panels whenever the train stops.
Yes, because they're just that, ticket sellers who do not have the same safety training as a guard. In an urban area where the train is generally quickly accessible to the emergency services/railway staff, that's one thing. There a no point in having safety training if you just go without it anyway. Buy in deepest darkest North Scotland or up a mountain/in a 3 mile long tunnel in the Pennines? Not a great idea if you ask me. The same applies as well - all these little shacks in the middle of nowhere having to be heavily modified to be operated from without a guard (rebuilt platforms/lighting etc) as the driver can't move from inside the cab without a heavy time penalty.