Unfortunately like most 'sports', it has been ruined by money, and the urge to win at all costs. The financial gains in athletics outweigh the risks of being caught taking illegal substances.
As has been said, if an athlete wants to compete at the top on level terms, then he/she will need to use the same 'aids' as the rest.
But the point is - if they do get caught cheating, they know the score - and they should be banned.
Yorks