All we have is the Gorn's justification for wholesale slaughter. Nowhere do our heroes negotiate with them. It was only stopped by the alien intervention.
But the point was that the possibility for negotiation existed, that it was an error to assume they were just unmotivatedly evil because they looked scary. "Arena" is basically the same story as "The Devil in the Dark," a subversion of the "scary-looking monster is evil" assumption by saying "Well, maybe they see us as the monsters."
Which goes against the intent. Star Trek is our future. That has been the intent, as well as shown with trips to the past being our past.
No. Again, it was never meant to be literally our future. People who write fiction do not assume themselves to be prophets; they know they're making it all up. Nobody who made Trek ever believed that Vulcans or Klingons are actually out there in the universe or that Jim Kirk or Uhura would actually be born someday. The point of fiction is not to lie to the audience, but to show them a satisfying illusion. The goal is to create a fictitious future plausible enough that you can suspend disbelief and allow yourself to pretend it could be the future while you're watching it. Just like the magician's audience watching a lady get sawn in half, they're not supposed to believe it's actually real.
I mean, good grief, even most non-science fiction TV does not literally depict our present, just a fictional world that resembles our present. Look at all the "realistic" shows where the US President is a fictional character, or where the foreign spies come from an imaginary country, or where the leading TV news network is VNN or JNN instead of CNN, or where the NYPD cops operate out of the nonexistent 12th Precinct and have 555 phone numbers. It's nonsensical to expect fiction to depict our reality literally. That's not what fiction is for. It's just meant to feel enough like reality that we can play along with the illusion.