I think I saw this movie on TV, or it may have been a play.  And it was long ago that I saw it — perhaps in the 60’s or 70’s, but might have been in the 80’s.

It centers around a progressive family — mother, father, and 2 or 3 kids.  Their adolescent [or teen aged, or even young adult living at home] son has a hobby, that he practices in the basement.  This hobby is the crux of the plot, and involves printing posters, that he hangs around town.  I seem to remember that he would go through phases, and his current phase was printing Socialist [or Communist] slogans — or at least some sort of content deemed subversive by certain members of the community, which is what led to a government agent [might have been FBI] showing up at their door.

The fun of this movie [which I believe is a comedy] is how the family deals with the agent, demonstrating to him, with their progressive, live-and-let-live charm, that not only does the government have nothing to fear from their son, who doesn’t even know what the verbiage on the posters, actually means, but that conservative paranoia is quite silly and if I remember right, the agent begins to second guess his whole career and there might even be a love affair with the daughter [which would suggest the “kids” actually are of adult age, and still living at home].

Anyway, I’m dying to see this movie again [or if there’s a book, or a play…], so if anyone can come up with a title, that would be awesome!