I'm not sure regarding "one hit from paralysis" but he failed to play at all in the 2009 season, so he was being drafted based on his season a full year prior. He was also not cleared for any type of activities until January before the draft due to the surgery. And just because he has been cleared does not mean he is unlikely to suffer the injury again. Also his agents word, especially Rosenhaus, means squat.
With the benefit of hindsight I agree, but with that benefit alot of things would change. Drafting a player with a serious back issue is a major risk, something the Patriots could afford & something I would not have been happy about had the Bills taken him.