It's not "their" route, it's just "a" route. The OP obviously found this too and if he chooses to share it with a friend, with a group of people, or everyone, it's his business and nothing to do with unknown people who may, or may not, be using the route.
Find it really hard to believe anyone has any kind of negative reaction beyond "damn, time to find a new route" on this.
It's not hard to imagine the negative reaction, just think that your action has consequences to others, sometimes negative consequences.
Would publishing a trade route on the forum or Galnet have negative consequence to the commanders already trading on that route? I think the answer is yes and we can all agree on that.
I was THE commander trading for over 3 weeks at XXX location (name of system withheld, as there are commanders still trading there, and even though I made trade Elite, I don't wish them ill consequences, even though they are my competitors) milked over $200M out of it during that 3 weeks. It was stable like hell. Then, one day, it ran dry within 3 hours, and I watched it got consumed about 3000T of gold per 10 minutes. Guess what? Galnet blasted it out in the public for a cheap thrill (the fun only lasted less than 3 hours.... That cheap....)
To be honest, most commanders are not very smart, they left soon.... They see literally a gold mine but couldn't see the potential and couldn't figure out how to trade. It took more than a week for the nearby systems to recover to a tradeable manner. Even then, some smarter commanders stayed to compete with me. Sure, it's now in the public trade DB (I know, I searched it in the DB.) But, 1. Do I ever need the publicity? Every time it gets blared out in the open, it ruins my weekend. What have I ever done to you to deserve it? 2. Evey time it gets blared out in the open, more smarter commanders stay to compete with me. I don't need more competitors. It is inevitable that other commanders will "find" my trade route, but I don't need you to accelerate it!!!
Time to find another trade route? Says easy! You know how hard it is to find such a good trade route? I made trade Elite, and I have never found another route that is remotely close to this one (not the one Beatz publicized, that one is not very good at all)! Just remeber, whenever you publicize a trade route, you potentially ruin some other commanders' weekend!
Do you think you are being generous by publicizing the trade route you outgrew? Yes, you are! But it's built on the bones of other commanders! All in all, it doesn't come out all that positive, does it?
Be considerate to your fellow commanders, even if they are your competitors!