So...
Let's imagine this idea is used by a PK gang - dozen of gangsters, all 21st level killers and armed to teeth - to lure the inexperienced or lone-wolf players, miners or even smaller gangs by calling for help, and when their prey joins encounter, bringing them down easy.
Or channel spams? Someone who doesn't need help at all could spam the channel "for fun", making other players angry. Trolls are everywhere, they even spam the GM channel.
What about such issues?
In a day or two, nobody would use this feature anymore, and all work would be in vain.