Sorry but you are completely wrong. 3 days after the rules changes a young lad was killed at Oakengates tunnel, if the driver had sounded his horn on this occasion the youth may still be alive now. On passing Craven arms at 90mph I sounded the horn as a train was in the platform as I sounded it someone stuck their head out from behind the train if I hadn't sounded the horn he would now be dead so safer certainly not - people friendly for noise pollution certainly yes.
What a strange example. If you had to cater for trespassers on the line you would be sounding the horn continuously, not just in tunnels. Your poor youth shouldn't have been in there and might well have been killed even if the horn was sounded
incorrectly on approach.
I must admit I do occasionally sound the horn when I pass another train in a station if I'm bowling along (sometimes a station seems a very crowded place when you get pushing 90 on a double track formation). I have on occasion seen people run across from the opposite platform to catch a standing train which makes me a tad uncomfortable. The same goes for a shunt on an adjacent running line. Not so much passenger train but you do see the guy with the radio on those strange freight trains (joke before I get shot down).
However, the rule book is a living document. It is constantly being reviewed and updated in response to various new issues and the removal of others. It will also be updated when certain issues no longer present a risk. When a new rule is added you are expected to adhere to it but you are not expected to perpetuate those that are removed - otherwise it would be an enormous unworkable thing full of old tosh from steam days.
The use of the horn seems an emotive subject to drivers. To many it's their favourite toy and they have their own slant on it. If you think about the whistle board, the very name and the fact it says W and not H says that it is a relic from steam days when some poor sod had to look down the side of a 30 foot boiler with smoke and steam in his eyes. He simply couldn't see most of the crossing but now you sit behind a windscreen with a wiper (except maybe 142s

) and the crossing user sees a thing that is yellow, as big as a gable end and has a light on it (except maybe 142s).
Your personal attempt to make the railway safer is perhaps understandable but statistically it has been made safer by other means as discussed above and better crossing management by NWR. They are always strimming on the approaches and fussing round them. The use of the horn has been removed in some cases for a reason and strictly speaking you should stop doing it where you are not required to. Now, common sense applies and if you suspect trespass around a tunnel then you would be acting professionally by using the "any other time deemed necessary" rule. Otherwise, any benefit is just to satisfy your obsession with your favourite toy........
.....I'm tormenting you but with a serious undertone,