Actually, I liked the Barnabas/Dirk confrontations. Have to agree that Barnabas wasn't thinking very clearly about his plan for Dirk. As others have mentioned, Dirk HAD been human at one point, and people would wonder who made him what he was.
Maybe Barnabas figured as long as there were no more attacks, everyone would think and hope the other vampire had disappeared, having found another place to victimize. But that would mean he'd have to hold his bloodlust in check and not attack any more doxies....I just don't think he'd be able to do it. No matter how hard he has tried to resist in the past, he eventually bites a victim. I mean, Barnabas couldn't afford to bite Beth EVERY night, or she would have suffered his fate.
I always wondered though, why Barnabas didn't hypnotize Dirk into forgetting? And how come Dirk's obsession with Laura is still going on? One would think her hold on Dirk would have vanished along with her.