You are correct that we had misinformation before the internet, but one would think that the business of genealogy would have progressed something beyond that point by this place in time.
If, as you say, sources are not noted in the family trees because the poster wants us to contact them, then why is it that we can never seem to get in touch with them.And, if we are so lucky, we are told they got the info from so and so and you can spend a month trying to find someone that will admit to handing out the information. Finally, we learn that they aren't connected to the family at all.
Ancestry owns Rootsweb.Rootsweb has a mechanism for us to make posts when we have information to correct something that is wrong in a family tree.There is no good reason why Ancestry can't take advantage of that capability.After all, they own it.No, Ancestry would rather keep bragging that they have the biggest genealogy website in the world and never mention that we may not get the right information.
I don't use the family trees at Ancestry or anywhere else on the 'net, but there are plenty who do.I think Ancestry, and every other genealogy site, should give us a way to correct erroneous information.In the process, we will be sourcing the material for them.