Stevie Wonder to Marvin Gaye's Family -- You Got Crap Legal Advice

Stevie Wonder thinks Marvin Gaye's family should take higher ground (see what we did there) legally speaking -- because their crappy lawyer is getting them into a lawsuit with Robin Thicke they can't win.

Stevie was fired up when we got him outside LAX, and says the fuss about "Blurred Lines" possibly ripping off Marvin's hit "Got to Give it Up" ... is stupid.

Stevie knows what he's talking about here ... remember he and Marvin were contemporaries during Motown's golden age -- and he says he's dealt with similar lawsuits himself.