It seems to me that just about every possible shadow of doubt is used to prevent halachic rulings that would classify a person as a mamzer. From my understanding after having read this paragraph on Wikipedia, if there is any possible way to discredit evidence of mamzer status, it will be done.
However, this sort of evidentiality, where any sorts of loopholes to discredit evidence can be used, would be regarded as unjust if applied to other cases because it is a standard of evidence that is impossible to fulfill. It would seem that more effort is taken to prevent people from being classified as mamzerim than actually trying to find out if they are.
What standard of evidence is necessary to indicate mamzer status? If it is higher than the standard of evidence necessary for other halachic rulings, what justifies the discrepancy?