The three Soviet KGB officers who met Oswald say it was indeed Oswald. Two of the three Cubans at the consulate say it was Oswald. The third, the consul, said the person who he met didn't look like the Oswald who appeared on TV and arrested for the assassination. Duran's description is off but she insists it was Oswald. Duran's phone number was found in Oswald's notebook/diary.
People on the bus to Mexico City say it was Oswald. People at the hotel where he stayed say it was Oswald. Leftist Mexican students say they met a person they think was Oswald. Photos given to the Cubans are of Oswald. The signatures on them were identified as belonging to Oswald. The signature on the hotel registry was identified as Oswald. A Mexican visa given to a Oswald had, according to handwriting experts, Oswald's signature on it.
Marina said he told her he went there. Oswald wrote a draft letter - his handwriting - where he discussed going to Mexico City and failing to get a visa. A typewritten letter - typed on Ruth Paine's typewriter by Oswald (according to Ruth and Marina) - mentioning the trip and based on the draft notes found was sent to the Soviet Embassy. The signature on the letter belonged to Oswald. The writing on the envelope belonged to Oswald.
On and on and on....
You can say all of this is fake, a lie, a deception. In which case: never mind. Whatever evidence is shown that he went there will be dismissed as false. What's the use of continuing the discussion?