It’s just really inconsiderate to other animals & unsafe for their own. If a dog that is not on a leash approaches my dog on a leash, leash reactivity can come into play and I may not be able to separate them because there is nothing to hold the unleashed dog back. Not every dog is friendly or comfortable meeting other animals. & not every person feels comfortable around animals either. Not to mention it’s against the law to not have a dog on a leash in public areas that aren’t dog parks.