What do you suggest, Admiral? Should we fire on unarmed, peaceful ships? Start the first interstellar war on sheer suspicion? We cannot prevent him from building the Gate without destroying that ship... and then we are at war.
You have a point sir. However, you should notice that the Charlies are not hesitating to violate our territorial integrity when they see it fit to themselves, despite all of the diplomatic baloney, sir. Whatever comes through that gate should be scanned, regardless whether we hurt the feelings of those alien bastards or not. Security first, diplomacy when whe have time and resources for such nonsense, sir - or at least have a bloody clue what those pea-brained xenoforms think they want with the jump gate.
Also, we should try to colonize into the other direction as well, sir. Procyon is safe from Charlie colonizing, but Ross world are not. There are no prizes for the runner up in that race, Sir.