Wikipedia's policy is to state the prevailing view among experts, while giving whatever weight is appropriate to minority views. Depending on whether the minority is one person (one "crackpot" if you disagree with that view) or a significant contingent within the field, the appropriate weight might be none at all, a brief mention, or a more thorough presentation.
The alternative is for a bunch of nonexpert Wikipedians, most of them pseudonymous, consisting of whichever volunteers happened to show up to edit that article, to constitute themselves as a review panel to adjudicate a dispute among experts. I pick the example of the climate change deniers because they're actually active on Wikipedia. They keep trying to weaken articles that report the scientific consensus about anthropogenic global warming. I don't mean to imply that you agree with them, but they would take the argument of the form you suggest and happily assert that the earlier incorrect AGW views have been disproved.
The professor who wrote about the Haymarket affair concluded his Chronicle article by expressing the hope that his analysis of the trial transcript would convince other experts in the field, and that his view could then be treated in Wikipedia the way he wanted. That's the correct approach. Wikipedia relies on the community of professional historians about the Haymarket affair, and relies on the community of climate scientists about AGW, and so forth.
The approach isn't perfect. If there had been a Wikipedia in Copernicus's time, the article on astronomy would initially have stated the geocentric universe as fact, then moved to mentioning heliocentrism as a minority viewpoint, and eventually (by some time in the seventeenth century) stated heliocentrism as fact and simply omitted any reference to geocentrism except as part of the subject's history. Wikipedia has made the decision that it will reflect what the experts currently say, rather than trying to identify an unorthodox viewpoint that will eventually be accepted as fact. Given the project's limitations, I think that's the correct decision.
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