Some will probably argue that it will encourage kids to use drugs knowing that the antidote is there in case they take it too far. This seems to be a common problem people have with preventives and other safeguards. (People make similar arguments against condoms).
I tend to believe that it's better to be safe than sorry. It's a pragmatic measure: If you have people overdosing, you should have an antitode present, all other factors are irrelevant. That said, narcan is just a band-aid solution, it's not going to tackle the actual drug problem that places like Akron have.