Once you find your comfort zone, you won't need anybody else to validate it. Experience will tell you what to do. If somebody's asking the question, they probably don't have the experience and probably shouldn't be taking the shot. How does one get that experience? Well...There's a lot of good rules of thumb on this thread already.
Why is this even an issue? Bow technology? Perhaps, but I believe that the main reason this is an issue is because we have the internet and social media and our egos. There is no requirement anywhere that we disclose the distances from which we shoot at animals, yet we all do. I always am curious and want to know how far somebody was, but does it detract from your story on social media or on here or wherever? Ignorance is bliss. Omitting details isn't lying in a situation like this. We're all here to learn from each other ultimately, so I guess one could argue that it's not our egos, but in the interest of full disclosure as a teachable moment that such details are disclosed. Either way, you've got to realize by now that if you're shooting at animals beyond 60 and feel the need to post it up, you're going to get some flak.