Isn't a spoiler bad for performance on our Yari?

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Spoilers increase downforce at speed (like adding weight) at the rear, at the expense of drag.With front engine front wheel drive cars, I'm pretty sure that a spoiler adds to the under-steer they already have. Under acceleration adding more downforce to the back would also shift more traction away from the drive wheels and increase wheel hop. It seems to me that spoilers are purely cosmetic for our cars (adding unnecessary weight and drag too). Granted, I love how they look on Yari , but I'm pretty sure there's not any real advantage to them. What do you guys think?