No matter what your position is on whether or not the NOP allegations are correct, I do not understand why there is not a system of lifetime bans for athletes guilty of cheating/doping. I think the athletes would all agree that this would be good for the sport (except those who have cheated or are cheating). Currently, an athlete cannot run fast without there being suspicions of them doping. In the case of Mo Farah, either he is doping and that is a HUGE shame, or he is not doping and everybody thinks he is doping and his reputation is being tarnished (I personally don't think he has cheated). It is hard to be excited about the sport if you can not ensure that athletes are clean and it is incredibly unfair to the athletes who compete clean. Lifetime bans are the only possible solution to this problem (they wouldn't completely solve the issue but it would solve it dramatically.)
Let's say there's a baseball player named B-rod and his goal is to make it to the major leagues in baseball and make a ton of money. Lets also say there is a two year ban for doping. Lets say he takes steroids to get to the next level and then makes 20 million dollars in first year. He then gets caught the next year and suspended for two years and then gets to continue making his 20 million a year thereafter, where is he being disincentivized to cheat? If the difference between being in the major and minor leagues is 19.9 million dollars/year why would he not dope to try and get into the minor leagues when he could make more in one year from the majors than a lifetime of minor league baseball?
Compare this to a system of lifetime bans. If he plays for a year, gets his 20 million, gets caught, has to pay back a ton of that money and can never play (or make money from) baseball again he would be much less inclined to cheat.
Right now rewards for doping outweigh the punishment. You have much more to gain in the years that you can slip through drug tests then you have to lose for the year or so that you are suspended. When the rewards of a behavior outweigh the consequences of a behavior, is it any surprise that things are the way they are right now?
If we create a lifetime ban, it would make the consequences of doping much heavier than the rewards the extra boost that doping may bring you.
In this system, the people doping would be the ones who are making poor financial decisions, rather than the ones making smarter financial decisions. Right now, some people are willing to make poor ethical decisions for smart financial decisions (which is despicable), but if we create lifetime bans, the smarter decision both ethically, AND financially would be to do it clean. In this case only the idiots would dope and we could be much more inclined to believe in the performances of our heroes.
I realize it is hard to compare baseball to running (especially in terms of salaries) but I think the concept is the same (granted on a much, much smaller scale).