YABVU
Perhaps the riders could be more polite but as you're not exactly behaving perfectly yourself I'd say it is pretty even on that score.
I have horses and dogs. Both dogs and horses can be unpredictable, and although you think they'll be fine you can never be 100% sure.
My DD's pony is a pretty bomb-proof schoolmistress, but even she has her moments very occasionally.
My dogs are also very used to horses, and have never batted an eyelid, but I still bring them back to heel and make them sit when horses (and cyclists, runners or other dogs) are passing. Why do I do this? Because although I don't think they will approach/ bark/ attack the horses (or cyclist/runner or other dog), I cannot categorically be 100% sure that they might do something daft for no apparent reason and I don't want to take the risk of hurting the rider, the dog or the horse for the sake of a few minutes.
You should have your dogs under control- the fact that you might have to "dive into the nettles" to get your dog makes me wonder how under control your dog is. I actually don't mind if dogs are on or off leads as long as they are under control and have good recall. I am not one of those people who think dogs must be on leads at all times and think they are entitled to let off some steam- but if you are going to do this in public places (such as footpaths or bridleways), then you need to be sure that your dog will come if called (accepting some degree of risk that a usually reliable dog can behave out of character).
You say your dogs don't approach the horses (so far) but how do the riders know that? For that matter, what is to say that although they have not done so yet at some point your dog might approach one of the horses? Or come out from the undergrowth unexpectedly? It's also possible the horse may be a youngster or have previously been attacked by a dog or just feeling spooky that day.
Your actions are potentially putting the rider, your dog and the horse in a dangerous position, all for the sake of a few minutes (and to make a point). Not sure it's really worth the risk, personally.