I mean, if you really want to take it to that extreme, why is the argument against facebook videogames and not videogame culture as a whole? Seems like in this case, Facebook is just a scapegoat.
What's more, games often help people connect to others, sometimes from around the world, in a shared interest. For people who are socially stressed or are going through a rough time without enough support in real life, this can be extremely helpful. And even for those who have plenty of social life, it's often fun to meet people in game.
I say this as a lifelong game player, and it's not to discount their positive effects - I think I'm a much better strategist and planner as a result of playing games as a kid.
It's precisely this property of videogames that allows so many people with similar problems to feel achievement.
A lot of videogames focus on instant gratification and variable time rewards. There have been some games focused on problem solving - games where instead of simply playing you'd find yourself spending 20 minutes looking over your handwritten notes trying to puzzle something out - but they're a minority.
I've had to put the kongregate minigames site into my own /etc/hosts file as 0.0.0.0 to stop myself playing the "Idle"/"Clicker" genre.
Positive games do exist, but they are thinner on the ground than they used to be. I think.
The problems come when something has a feedback loop which promotes more usage beyond normal usage. Alcohol has this, and so does heroin. Different games have this to different degrees. Like most things I've mentioned, different people are susceptible to this to different degrees, which complicates the issue.