They are wrong in saying that it does not have any paradoxes. If we send a message to the past, that says, "kill baby Hitler" then our time line would be forever different.
Also, as Carl Sagan once said, it is almost certain that time travel cannot exist. If time travel were possible we would have been visited by a future person already detailing how to make such a machine, or what to look out for. The same can be said about the messages. If this really is possible, then how come we haven't got messages yet? All they have to say is, ok, lets set up a camera to capture the messages in this ONE spot, forever. It will ALWAYS be in THIS spot at exactly 12 midnight from NOW ON. Then all they would have to do, is set up that camera, and wait for the future people to send a message to that spot. Tickle me retarded, but this isn't possible.