Despite hating the Legion, Arcade Gannon will travel with you to The Fort. However, you can spin it as a positive if you say the right thing. What do I say to Arcade Gannon at the fort?
You should say to Arcade Gannon at the Fort: “Let’s just listen to him, figure out what he’s up to, and get out.” This will earn you 2 “history points” which improve your companionship and lead towards Arcade’s quest and perk.
Arcade despises the Legion, so it’s probably not a good idea to bring him to the Fort at all.
What to say to Arcade Gannon at The Fort
Arcade Gannon, member of the Followers of the Apocalypse, detests Caesar’s Legion. He makes it very clear at the start of your companionship that he’d leave you if you choose the Legion.
Yet, when the Courier is invited to speak with Caesar, they are free to bring Arcade along.
Once you enter Caesar Legion’s Fort with Arcade Gannon as a follower, he’ll stop to speak with you.
Arcade asks what’s going on here, and implies that he’s “the Vergil to your Dante.” He goes on to say he’d like to assume you’re here out of academic curiosity, but he’s not so open-minded that he’s “lost his brains.”
Your response will determine the amount of “history points” you earn with Arcade. These points are invaluable in progressing your relationship and unlocking his companion-quest and associated perk.
“I just want to hear Caesar out” earns 1 history point.
“Let’s just listen to him, figure out what he’s up to, and get out” earns 2 history points.
“Once we get close to Caesar, we can strike” earns no history points.
“With how messed up New Vegas is, do you really think Caesar has nothing to offer?” actually loses you a history point. You earn a second subtraction of points if you double down on this idea.
So that’s the answer. You should say to Arcade Gannon at the Fort: “Let’s just listen to him, figure out what he’s up to, and get out.”