Hi Mary,
I don't think many here actually object to Ancestry altogether. It's really "Ancestry Member Trees," "U.S. and International Marriage Records," "Family Data Collection," and many of their other databases, that are user-submitted, unsupported, unverified, and often just plain wrong. FamilySearch has similarly dubious sources; "Pedigree Resource File," "International Genealogical Index," etc.
The other problem with Ancestry is that even if you cite a good source there, (census records, images of wills, ship's manifests, etc.) the links are inaccessible to anyone who doesn't pay Ancestry for access. Whenever I see these, I will replace the link with a free link to FamilySearch or another free source for the same document if I can find one.