Why doesn't Ancestry do better quality control (or let us do it)?

One thing that disturbs me is that I keep finding errors in the great-grandparents in terms of who their parents are.   Specifically, Isaac Tousignant (a 4th great-grandfather) had the wrong parents, which meant that designations up the tree (and then down again) were all wrong.

That took some time to clear up.

Apparently in my early over-eager efforts, I made some huge mistakes.   I'm not surprised, and this leads to a complaint I have about ancestry.com:  there's NOTHING in the service that allows anyone to tag people or data with any type of "quality" flag.   Why? 

What I'd like to see, however, is a flag placed on specific people: a "completely verified" badge that would let people know that when they encounter a person on someone else's tree, that blindly including that person in your tree is "safe" (and helpful).   I've been burned by bad data (as mentioned above), and I think that one of the nastier problems with the service is that newbies can - in their over-eager quest for checking out "leaves" start compiling (and thereby propagating) bad data.

Wouldn't it be better to offer something that gives confidence in tree building?  Not only that, but it would allow aggregation of different sources of data that could be mapped into an "official" tree.