It worked for me. He's pretty good looking.
I think the initial point of the movie is a weird take on how veterans and families of veterans are screwed over. Dave is their son and they are his family since he can't return home. It's not that Dave is charming, it's that Dave fills the void of the dead son. So, they accept him regardless of logical response to a stranger or his charisma.
They kind of dump that idea after half an hour (at least for the audience) because we know he's evil once the father's coworker dies and he attacked the kids in the bar. By then, I think the movie wants us to think of Dave as this weird, programmed weapon in a Rambo First Blood "look what they did to me" way.
I don't think the movie accomplishes either of these goals, but I think that's what they are aiming for. I think they were trying to elevate an action thriller as opposed to, again, First Blood with is trying to make a action thriller out of a drama on vets returning home (although, I don't think First Blood totally accomplished it's goal either).