You've got it backwards. No effect is being applied to soap operas. It's the tvs that are applying an effect. Let me explain.
To fool the human brain into believing that a series of flashes are a continuous, moving image, the flashes have to come at a minimum of between 50-60 Hz (cycles per second). The chemicals available in the early days of motion picture film simply weren't fast enough to get a good exposure at that speed--and it would have taken a LOT of film. (In 35mm, that's almost 1.5 meters of film going through the camera every second!) It was realized that you could cheat by flashing the same frame multiple times. Standard motion picture film, though only shot at 24 frames per second, sits behind a spinning shutter that looks something like a radiation symbol: As it spins, it flashes each frame three times: 3*24=72 Hz.
When video came along, it used a different method of cheating. Video cameras would record (and tvs would play back) every other line of an image, alternating between even and odd at (in North America) 59.94 Hz. 896
This means that effectively tv was playing back motion at ~60Hz, rather than flashing the same frame 3 times. It's a subtle effect, but it's one that our brains can sort-of detect: The motion in a native video image is "sharper" than film.
Modern HD tvs can display full frames of video at 60 Hz. To show off this feature, some idiot one realized that, by adding a cheap frame interpolation chip, any source--including movies shot at 24 fps--could be nudged up to 60 Hz. (I say cheap because the same frame interpolation was already available as a transition on the first generation of DV camcorders back when I was in college.)
Where soap operas come in is their speed of production. To save time, they've always been shot with studio cameras, on video. Contrast this with bigger budget shows like "Gilligan's Island" or "M*A*S*H", which were shot on 16mm film and then transferred to video. It's entirely cultural. We've grown up with "big budget" material having that slower, more dreamlike motion of low frame rates, while soap operas have a sharper, jarringly more real motion. That's the "soap opera effect." 896