Going through this thread, I teeter-totter on the fence...
On the one hand, they're people and they have good/bad days, moods, you name it. Likewise, it must be an odd, surreal, or even weird experience at times.
On the other hand, they're being paid a handsome sum of money to be present. And depending on who they are, that sum of money can be what is to 99% of us a few months to over a years salary. It may be chump-change in Hollywood money, but it's enough to get them on a plane, fly cross-country, stay at a hotel, and interact with a few hundred people, so it should be enough for them to do their best to act their best. Even if they don't always succeed.
In my experience? The vast majority of them do so.
It's the exceptions
that don't. The exceptions we've mostly discussed here.
I've met 60-odd actors, 75-80% of them Star Trek. Virtually everyone from the first four casts and tons of guest stars. And out of them maybe 5-7 of them left a bad impression with me, while the other 53-55 left me satisfied.
As to the ones who I consistently hear bad things of? Who can say why they are that way. Why they take the gig, take the money, show up, only to act like that time after time. Is it just the greed, just the money? Maybe. Maybe they don't know/think they're acting in a way that's deemed badly. I suppose none of us will ever know.
In the end though, of all those I've met (autograph inventory list
that marks who I've met for those curious) the majority where worth the time, money, effort, energy, et cetera.