That's a nice theory but Reagan didn't let that stop him re: Libya.
You'd also have to believe that every little bit of evidence would compromise security. To add insult to injury, you'd also have to believe that the Prime minister of England is more trustworthy than the American people when it comes to this evidence. The quote you provided shows that even the evidence that does exist cannot be linked to bin Laden in any substantial way. Laden has denied his involvement. Not that I believe him to be trustworthy but I don't find our government officials to be trustworthy either. If you're willing to accept the word of government officials who have more to lose by telling the truth than lying, that's your call. I don't buy it.