I don't see anything wrong with breeding grouse for shooting. They are a major food source and income in poor areas. A farmer's mum I know is fed up of making grouse and pheasant dishes, but that's the way it is. It is food.
Birds of prey shouldn't be poisoned, I agree. That is a question of policing. A balance does have to be achieved and so much conservation of birds of prey is leading to a bit of an imbalance, it seems to me. Not an expert on this by any means, but if you preserve, say, Red Kites, then they will take young birds. I get really quite upset about the poor moorhens losing their chicks year on year to a local sparrowhawk - but that is nature. It is not kind, but grouse moor preservation does keep a balance. I like to walk our moors and want to keep things as they are. It has worked for a long time. I expect to be unpopular for this, OK. 'night :)