I have been very fortunate that overall many of my far ancestral information has been documented by someone, somewhere, some long time ago. Whether it was the New England books, or Virginia ancestral lines, someone, somewhere has documented something. It only took me a few generations going back to find most of these! If they hadn't shared their information in old tomes catching dust, and if those same books hadn't been shared, I wouldn't have made the vast discoveries I've found. It's exciting, and I guess it gets me carried away!
On the other hand, I have a few branches where I haven't been able to get very far back. One, I think is because he (Samuel Johnson Newell of Maine, for example) was adopted. So the YDNA that my male Newell cousin did for me didn't provide any clues.
As far as information that could be incorrect, I take EVERY bit of information with a grain of salt. I add to my tree on ancestry sometimes with caution and sometimes with whimsy.
My hope is that others' information is published and/or shared, how could I have come to know so much if it hadn't been? I think most who are interested in genealogy are aware that it is always a work in progress. Whether it is dates or spelling of names, the information varies. At least that's been my experience over and over again.
I have several cousins who were adopted. It's confusing to figure out where and how to list their lineage. They ARE part of the family. They openly admit that they were adopted. I think family tree data could (and should be) be modified to more fairly allow and/or reflect such details IF someone so desires to reveal such information.