The Nirvana fallacy is an attempt to compare a realistic solution with an idealized one, and dismissing or even discounting the realistic solution as a result of comparing to a “perfect world” or impossible standard.
This reasoning ignores the fact that the solutions are often good enough to meet any reasonable standard. Furthermore, the fallacy often focuses on one single standard of an idea or thing without regards to the other qualities that may be important in evaluating that thing or idea.
In addition, the Nirvana fallacy can lead someone to ignore an unbiased evaluation of a risk versus benefit analysis. One could focus on the risk, demanding that it be completely eliminated, even if the benefit far outweighed the cost.
The MMR vaccine has a 1 in 1 million chance of a serious adverse event. Thus, it should be considered so unsafe that it should be removed from the market until a vaccine that never has an adverse effect is available.