Your 100% correct, However unless you set up a FWD car for tremendous oversteer at the limit, a rear spoiler just adds drag and increases weight, (neither is good)

one companay famous for actually using a functional spoiler on a FWD car is Real time Racing,



but those cars were specifically designed with such stiff rear suspension to REQUIRE that down force to maintain stability. they were known for their tendency to over steer on slower corners.

so do I realize.. of course my friend, I have been building race cars for over a dozen years. but I've driven my sentra at sebring with it's Factory "airbrake" installed and not installed and with the spoiler removed I can acheive 3 more MPH at the end of the back straight. (that's why we ran OLOA07 with it off the car)

but my car is also driven on the street so I cannot tune it for rear down force, I'm tempted to invest in a splitter and canards, but can't justify the advantage over the pain of driving that every day.