Should doping in sport be legalised?
Of course it shouldn't be legalised, because legalise drugs in sports means good athletes will not compete with their own power. And bad athletes who takes drugs will win against the good athletes if good athletes are not druged.
Will it ever be possible to stop athletes breaking the rules to win?
Yes, it will. Only if associations start to punish athletes who brake the rules, and according to the level of the damage they decide to bann forever the athlete.
Are athletes who take drugs cheats or are they victims?
They are cheating, they are victims of pressure, but they know the limits and the rules. Everyone is responsible for their own actions.