OK, the following is a not-so (IMO) hypothetical situation...
Imagine being one of the best 10 or so hitters in the game...your numbers are consistently in the 28-32 HR range, you hit around .290-.300 or so and you're a good fielder to boot.
Then along comes someone who really couldn't hold your jock...and after several years of middle of the road offensive seasons they hit 30, then 35, then 50, then close to or perhaps more than 60 HRs and garner awards, money, adulation and media attention...and you've learned that the individual's accomplishments were fueled by performance enhancing drugs. At the same time, you learn that more and more players, even the pitchers you are facing, are using something.
Seems it would be awfully hard NOT to go down that same path.