The short answer is people don't need any knowledge, they don't need to Google about feeding horses, if they just look, admire and keep going they don't need to do or know anything else.
Personally I'm not bothered if someone wants to stroke his nose or neck, but if you choose to do that without any knowledge then if you get nipped, shoved by his head or your toe stood on, it's on you because that's what you chose to do and that's a risk when you're around an animal as big and strong as a horse, and that is just common sense. I don't fuss horses I don't know precisely because I don't know them, and I do have knowledge and can read body language.
Do people randomly go around putting fuel into someone else's tank because they like the car?!
No, they don't, but for some reason horses are seen as public amenities and a free for all, we try and tell people the damage they could cause in the hope that it will appeal to their better nature and they don't want to hurt the animals, and as I said before, because people asked to stop demand to know why?! They might not have any interest in horses, but some will demand the knowledge, then refute it without a second thought. Simply because they want to do what they want to do and they aren't the one facing the potential concequences.
I mean I could talk all day about my horse, but apparently we're unreasonable for expecting people to heed signs or verbal requests because they can't be expected to have knowledge - they don't need to have knowledge to heed a sign or request asking them not to feed a horse, or any other animals for that matter, they just need to not do it.
There are campaigns, I'm part of one "Stop feeding our horses" it's on FB (Twitter and Instagram I think too but I don't have those) and there's posts and it's shared around a lot, I have signs up along with a couple of other owners with fields in the area, I ask people face to face when I see them, they're on private land with two gates (both locked) from the road, a hedge, fence and electric fence between them and the road and a 'barrier' electric fence along the fence that adjoins a footpath as well as the actual fence with electric wire along the top of it.
People climb the gates, and a neighbouring farmer has found people putting their coats over the electric wire and climbing over the fence into the barrier bit to get close enough to lean over and feed or throw food in.
The BHS has a section dedicated to it with printable signs, they have run campaigns, local press here ran ads and sections online and in papers, there have been news reports and segments (and I think one on Country File) I've been to my local farm shop today, big poster in there.
The problem is people ignoring it all, and the only way to change that is to have some sort of concequences attached, but even then people don't learn, dogs can be shot for worrying livestock yet we still have reports of them being worried, hurt and killed by loose dogs.
I've lost around a 3rd of my grass to these measures, I've taken responsibility, it's cost a fair amount of money and time, I'm being proactive, as from her posts is OP (and many others) and you bet it's frustrating to invest all that, still have people do what they please and ignore it all, and then someone like you come along and reckon it's still our fault and the people doing it bear no responsibility at all, poor things just trip and fall into a double fenced field and the apples/carrots/crisps/McDonald's jumps out of their hands and makes it's own way to the horses!
And that we're apparently not allowed to be worried and frustrated about that, or annoyed with the people doing it.
Well sorry to disappoint but I am going to be worried, frustrated and annoyed about it, and I'm not going to stop taking about it either - because it raises awareness, every thread like this there's at least one person who says they didn't realise and won't do it again - that's one (or more) less horse at risk, and although I prefer not to use the word moron (my go to is idiot) I'm not going to excuse these people their responsibility or pander to their entitled attitude because we've 'lost our connection with the countryside'.