Why should the standard be the quality of a professional genealogist, or the same qualifications, when most of us at WikiTree are not doing professional genealogy, nor professing or attempting to do so?
WikiTree terms of service, Honor Code, and style guidelines determine the standards at WikiTree. And those standards are to cite our source documentation so that other can find the records and judge them for themselves. Additional WikiTree standards are to make our research accessible to all levels of ability and interest; as WikiTree is a website, online accessibility to records is a presumed preference.
While the trees at other websites, including Ancestry.com, are not, themselves, source documentation (as per WikiTree policy), many of these websites also include source image repositories. These images, by WikiTree standards, are considered acceptable as proxies for the actual hard-copy records. Ideally, the citations for these images will include the repository for the hard-copy records, too.
Whether one is a WikiTree newbie or a grizzled veteran, most of us (my opinion) don't aspire to be professional genealogists; nor do we expect professional-grade work. If we did, we would hire professionals do research our ancestry; only then, would we expect professional-grade work.