In an ideal world, all athletes would compete on a "level" playing field, particularly in the amateur ranks where sports is "supposed" to be an expression of the collegiate spirit. However, the reality of college sports is that it has become big business, both for the players and for the schools involved. Players feel tremendous pressure in particular sports to succeed and gain fame, which in certain sports can lead to large professional contracts. People increasingly have a sense that drug use is not isolated to a few select athletes, which has caused it to receive a sort of passive acceptance over time. Still, there are a lot of reasons why drug testing is difficult. While one doesn't necessarily want to say that drug testing in college is a bad idea, there are certainly some challenges to overcome.
One major difficulty with drug testing is the technology that is connected to the problem. If a governing body were to come up with a list of banned substances, scientists and athletes would probably find a way to start using something else. Many of the drugs of today can be designed in a such a way that they are not easily detected. In addition, there is the issue of agreement between various governing bodies, and consistency would be a major issue. Technically, an over-the-counter painkiller offers a chemical advantage so there are often blurred lines when it comes to what should be banned.
Another major issue is the financial toll that drug testing would take on college sports. Testing bodily fluids for particular substances is not always cheap, and not every school has the financial resources for widespread testing. Professional sports leagues may be able to afford certain amounts of testing, but colleges do not always have the same budgets. Some smaller schools might be severely hampered if they had to bear the brunt of the cost. Therefore, drug testing might be a good plan, but many ideas have good intent and still lack the funding to be truly implemented.
Root of the problem
Again, the idea of drug testing and having some assurance of fairness is a good concept. However, the logistics, cost, and implementation is a definitively difficult task. Mandatory drug testing is one way of dealing with college athletics, but anytime there is competition, humans will look for an advantage. Unless people figure out a way to lessen the desire to win, there will always be a temptation to seek an unfair advantage, which makes drug testing just a symptom of a much larger problem found in the nature of humankind.