Seeing my three biggest positions are ARIA, MDVN and PCYC, my portfolio would very much disagree with you, to date at least. :)
You could make the same argument about drug development in general - clearly most drugs are going to fail. The exceptions are not, and it is our job to find the exceptions before Wall Street does.
First, like Peter, I'm heavily biased as the bulk of my biofolio is oncology-focused. But, I would submit that cancer-drug candidates may be a sucker's bet if you just plan on buying and holding long-term. I am by no means a short-term trader (you know I think TA is bunk), but there should be plenty of opportunities along the way to play the inevitable ebbs and flows in the biotech sector.
Too often, I feel that way about most, if not all, biotech stocks. The real winners have beem few and far between. For every AMGN, BIIB, GILD, etc., there have been probably twenty that have come and gone. Bty it sure has been fun to follow.