1. $...maybe so, maybe not. A few years ago, I may have thought that way, but not now. I didn't see a big walkout of fans after Palmiero got popped. Actually, the reverse has happened. Attendance seems to be great, and Raffy has resorted to wearing earplugs to muffle the boos. I think that the vast majority of fans are fed up with seeing Godzilla hit (or pitch).
2. The main culprit behind not having a "one strike, you're out" policy would be the players union. If they were serious about cleaning up the game, they would agree to ditch urine tests and agree to blood testing. Why? Many supplements, including Human Growth Hormone, are only detectable in blood... not urine.
Plus, there's still a lot of gray areas in what is allowed, and what is prohibited. How? It's a miracle of modern chemistry. Take a prohibited steroid, tweak the chemical structure a bit, and it's possible to create a different designer drug that has all the benefits of the banned substance with the additional benefit of being harder or impossible to detect.In essence, you're not using an illegal supplement, because it isn't the same... it's close. It's easy to punish a player for testing positive for a banned drug. It's a lot harder to punish them for using a "molecularly similar" drug.