It's not.
It's not pro-town to do,
And is inheritantly anti-town in nature,
But it's not scummy.
Why?
Because people do it all the time, regardless of alignment.
Then what do you do with a lurker, if you can't call lurking scummy? Just out of policy?
Wrong.
You don't lynch lurkers. You don't lynch people who've flaked, or are V/LA. Not on lurking alone, at least.
You wait.
Because lurkers have one of two things happen.
Either
1: They're inactive.
Eventually, said inactivity will frustrate the mod to the point of replacing said inactive lurker. Normally with a pro-town appearing active player. Instead of a lurker, you suddenly have a pro-town player.
Good to happen.
or
2: They catch up. Lurkers are normally lurkers because they can't catch up with the game. When the game is getting ten pages per day, even some legends at posts can't catch up. They fall behind.
Or they go V/LA. Either works, but they have the same result:
They Are Not Caught Up.
How they deal with it?
They lurk. It happens even to the best of us.
But eventually, even if it takes a month for it to happen, and five or six prods, they'll catch up. Eventually, when their schedule's clear, when they have no other projects to work on, they'll catch up.
And once caught up, they'll contribute. Actively scum hunt. Be a pro-town, extremely active player.
References:
Newbie 742. Ting, Kronos, and Caleb all flaked (Not to mention, my predecessor early on). Only one of them was scum. They were replaced later on by more active players (with one exception).
Maturin and PPP (Caleb's replacement) were both kinda lurking. Barely contributing anything, really. Both of them were pro-town.
763. I fell six pages behind. Kinda lurkerish, no? I was pro-town.
Both of the scum lurked/flaked as well (in one case, TWICE), though.
Mini 760. I replaced someone who flaked (said player wasn't particularly active and was slightly suspicious to most. When I came in, I became fairly active). Jebus was essentially lurking most of the game. Gorrad nearly got replaced. And that's just what I can think of off the top of my head. Only one was scum.
Newbie 762. Two pre-game flakes. (Both Pro-town.) At least two more after that. (One pro-town, one pro-scum.) The only lurking was from MiteyMouse, scum, though.
Polygamist Mafia. Only pro-town players flaked. (There was scum lurking [me], though.)
Lynch All Lurkers had special game mechanics preventing a good deal of lurking, but several players were replaced. Only one of them was scum.
Newbie 779. Three players flaked. Two were scum.
Two people were lurking, one scum, one pro-town.
Mini 791. Several lurkers/flakes. One Mafia flaked, one SK flaked, two pro-town players flaked. Several players lurked. (Like me.)
Cubic Mafia. I'm not going to go into most of the game, but I can tell that when I replaced someone who had to flake due to V/LA, I instantly helped nail the last scum. That's a change from a player who was inactive most of the game to someone extremely active.
Open 148. It contained several lurkers. CJMiller contributed almost nothing at all. Iamausername initially wasn't posting a lot. A lurking accusation was thrown against me. (All town.)
Sotty7 and Caboose (Last scum, Werewolf, respectively) were lurking, with Caboose eventually being replaced because of lurking. His replacement, extremely active and fairly pro-town in comparison to Caboose.
Now, while those might not be the best examples, I think it proves the point well enough.
You don't lynch lurkers.
Night-kill 'em if you want 'em gone that much,
Or just wait for mod intervention (replacements),
Or just have the patience to wait for the lurker to catch up so they stop lurking.