Well said. I'll add that no matter how strong a man is, his threatening to take out an entire family one by one at some unspecified date (perhaps weeks away) is ridiculous and unbelievable. There are just too many factors to stop him. People would run away, especially after the first throttling took place. Granted, you want to avoid even that first one... Adam's counting on Barnabas's desire for secrecy to be absolute, and Adam doesn't even know Barnabas's biggest secret, so he can't spill much. It's bad for Barnabas to have some beans spilled, but worse than what Adam's making them do? (But then, Barnabas isn't doing it personally!) At what point do you say, screw it, I'm tellin'?
Okay, I guess he would do anything to keep all the questions from arising.
I don't know all the things that could be done about Adam's overblown and insanely open-ended threat, but Barnabas could think of plenty. Perhaps privately-hired security goons to overpower and confine him, who would keep their mouths shut? Anesthetic darts? I don't know how Barnabas has money, apart for a handful of jewels, but he has it. Call Animal Control? Sell Roger on the idea of armed security guards for some made-up reason? (Barnabas can't have Adam hurt, but the sight of the guards could change his mind.) Do some Carribean voodoo he learned when he was young?
Really... worldly, very grown-up Barnabas ought to have laughed at Adam's threat. Really, Adam thinks he can hover in some hiding place they'll never find, indefinitely, and strike down everyone in Barnabas's entire family anytime he wants, now or months from now, force Barnabas to dig up bodies and stitch them together in his basement (If it comes to that, though, he's having the help do it!), then after it's over, he can just walk off hand-in-hand with his custom-made mate into the sunset, unmolested?
Is Adam going to go through his life threatening everyone's family whenever he doesn't get what he thinks he deserves? His boss at the Seven-Eleven's really going to like that. I think the writers were thinking of Adam more as a "movie monster" and therefore as untouchable and unstoppable, when really he's just a very big, strong (unarmed) man, whatever his origins.