If you have no clue, then why are you trying to convince someone?
TV looks bad on good monitors because it IS bad, low resolution, grainy, blurry, noisy, right there in the source signal. It's only that "normal" TV tubes are slow and low-resolution enough that you don't notice - while on a quality monitor, you will.
That's why HDTV is being introduced.
Anyway, when you're feeding the TV signal into a PCI TV card, and let the graphics card render and merge it into the computer's main display, you are doing NOTHING differently than a standalone LCD TV unit would do - only with hardware you already have, and with more usefulness (like recording to harddisk etc.).