The government was entitled to promise that it would be bound by the advisory result. What it could not promise is that it would be legally bound. Well, we know what politicians' promises amount to, but in this instance they are actually, so far at least, honouring their promise to be bound. They don't have to honour it and there's still a small chance that they will have to renege. Cameron was not entitled to promise that article 50 would be invoked immediately in the event of a leave vote. Had he for one second thought that he might have to deliver on that promise, he would never have made it. Idiot.