In addition to the above, the availability of award seats on sold out flights is usually 0. Maybe you would book the 50k premium awards to gibe you more availability. Enough people do this, adn NW no longer allows you to recredit for free. As soon as enough people scam an airline into loss of revenue, the airline cracks down hurting both you, and every other person who has that perk.
Sympathy from other FT members for you will not be great as you may take the seat that they wanted to buy or redeem on either.
Legal fraud is still unethical.