"They are sent from Mordor," he says flatly, "and they fight with terror as well as blades."

Then, remembering that he's speaking to one of the few people in Middle-Earth who's never heard of Mordor, he adds, "From the Dark Lord Sauron, to kill us or worse."

Gord has no more idea who the Dark Lord Sauron is than about Mordor. As far as epithets go, and by demonic standards, Dark Lord is practically wholesome.

They're not telling him why these Black Riders are after them, or asking for his help, or even saying they don't want to fight them, per se. Fair enough. He does have a selfish reason not to want to leave, because these people are his only source of information right now, but if they're attacked while he's there it will be much harder to convince the attackers that he's a neutral party.

...wait. "Merry. Translate what I said." He picked a good target for Share Language, because Merry speaks unguardedly, but clearly not the best one for coordination during a possible fight.

"He says - he says -"  Merry gulps, and then repeats in the Common Tongue, "if we want to fight them he'll go away or stand back - and he doesn't know enough about the world to tell whether to help us or them unless we convince him - will they even let him stand back?  I guess they didn't kill everyone at Bree, but -"

"You really don't know whether to help the Black Riders who fight with terror!?"

"They left people alive because they were after bigger prey, or so they thought."

Aragorn purses his lips. It goes against his instincts to tell a stranger anything about the Ring, but Gord already saw that it was magical - But then he doesn't know how Gord would respond to any hint of "they aren't explicitly trying to kill us," and the only truthful way he has to answer that is by explaining how the Ring would increase Sauron's power to kill or tyrannize everyone. And saying that - saying anything to tempt Gord after the Ring himself - might ruin everything.

"What do you want to know!?  Those Black Riders have been chasing us ever since we left Bag End - they've been putting magic on Master Frodo and terrifying us all - they tried to kill us - I don't know what they did to poor Fatty Bolger -"  Sam throws up his hands.

"I don't see how fighting with fear-spells is worse than just stabbing you to death. You say they tried to do that too, but frankly you don't seem likely to have fought them off with your daggers." Not unless those riders are a bunch of first-circle wizards afraid to ride into melee - no, focus. Gord crawls back from the cliff-edge to where he can stand up and fix Merry with his glare.

When Gord said he'd leave, they didn't say they'll go after you when you're alone. The Black Riders have been chasing them for a while, but not attacking others. If he leaves now he should be fine.

These halflings are acting like they're still under a fear spell. Gord's tempted to round them off to civilians - noncombatants who don't want to fight and should be given the benefit of the doubt - except civilians don't normally go around uniformly armed with magic daggers. Maybe they're just rich, but then where are their servants, their guards? Or - no, he shouldn't assume; maybe magic weapons are plentiful and cheap in this world, and any real fighters would be dripping with magic items.

Merry doesn't look like a real fighter, unless he's a very good actor, but everyone has to start somewhere. Gord has Remove Fear prepared, but it'd be silly to spend it now and not during the potential fight itself.

"Translate this. You don't want to tell me why they're after you. That's your right. But I won't fight on your side just because they're Black and scary. If I help you, and you kill them, it's as if I've killed them myself." He's not going to explain how fighting purely in defense makes the fight more dangerous, he's already straining Merry's capacity for translation. 

"In a few minutes my spell for understanding all tongues will run out. Only you will be able to translate for me, until tomorrow morning. I'm inclined to come back in the morning, heal any survivors, and maybe try talking to the Black Riders then and hear their side of the story. Do you not want to fight them? How could I trust you not to kill them, if I help you defend yourselves? Translate exactly what I've just said." And give the rest of his party a last chance to say something more useful.

"He says he won't help us fight without a reason more than they're black and scary - we haven't said why they're after us - he doesn't see the difference between fear-magic and daggers - and -"

Merry's impatience with translating rather than responding runs out.  

"We didn't try to fight back - we hid!  I picked up this dagger a few days ago and I still haven't used it for more than cutting our way through the marsh!"

Frodo respects how Gord wants a reason... even though he's strange enough that the reasons that make sense to them somehow don't to him.

"We've been trying to avoid these Black Riders; it's not like we've been using magic or daggers, and... I don't know how fighting back is going to work, unless Strider's hiding something, but we can't just let them kill us this time."