I am certainly not a fan of tanking as the draft results of perennial basement dwellers has been less than stellar. There are other reasons too (and I am sure you have thought of all of these Kirby):
- Its about who you draft when you are on the board more so then where you draft. While the success rate of top-10 picks @ QB are better, it is still not a science and recent history has shown that competent QBs can be found after Round 1
- Most QB-hungry teams have a terrible record to begin with (duh) and have had changes to the coaching staff. It is tough for a new coach to sell a tanking season to the fans. See McAdoo
- Financially it is a bad choice for the owners and they have to be totally on board to sacrifice a lucrative season in the hopes of future glory
- You do face the race-to-the bottom scenario when you may tank and still not be in a position to draft the QB you want
Having said all that, this is a great season to end up with a top-5 or top-10 pick, if you are desperate for a QB