Scholarly expert on the Haymarket riots tries to edit the (top-ranked) Wikipedia entry for the same, is violently rebuffed by community editors. In short, anyone can edit, but you must play by the rules:
So I waited two years, until my book on the trial was published. “Now, at last, I have a proper Wikipedia leg to stand on,” I thought as I opened the page and found at least a dozen statements that were factual errors, including some that contradicted their own cited sources. I found myself hesitant to write, eerily aware that the self-deputized protectors of the page were reading over my shoulder, itching to revert my edits and tutor me in Wiki-decorum. I made a small edit, testing the waters.
My improvement lasted five minutes before a Wiki-cop scolded me, “I hope you will familiarize yourself with some of Wikipedia’s policies, such as verifiability and undue weight. If all historians save one say that the sky was green in 1888, our policies require that we write ‘Most historians write that the sky was green, but one says the sky was blue.’ … As individual editors, we’re not in the business of weighing claims, just reporting what reliable sources write.”