Ancestry shouldn't care and neither should you. It is not your tree. How people use Ancestry's family tree system is completely up to them. If they want to believe a demonstrably incorrect conclusion is true, so be it.
Someone who does not care about the accuracy of information on their tree at the level you do, will not suddenly gain clarity and new-found-perspective on research methodology by simply presenting them with an argument or evidence demonstrating the error. They have already set their bar where that is concerned.
You may as well ask Ancestry to do something about all of the forum posts that contain spelling and grammatical errors. Some people care and some do not. Handle it the same way. A kind note: "I think you meant..." or in the case of family trees, "I think that photo is of someone else." Or just leave it alone and move on.
I care about accuracy. I love comments and criticisms I have received over the years. But Ancestry doesn't have to do something to protect me from the inaccurate information out there. For anyone who actually cares about accuracy at an elevated level, we already take the necessary steps to filter out these trees from our research. So there's no real need to police them. The only ones who will get bunk information from them are others who are already lax when it comes to expectations of accuracy. So if they don't get inaccurate information from Ancestry, they'll get it somewhere else. It is only a true problem for those who don't care about it being a problem in the first place.
And so what if they get it wrong? How many of those personal family legends have been debunked and proved inaccurate thanks to modern research tools and methods. Pervasive statements of inaccurate family history have been around for ages.
So that sketch of my 5th great-grandmother was actually her sister and numerous generations had it wrong. Is that a big deal? Are their lives for the worse because they didn't know the truth? Family history is rife with inaccuracies. We shouldn't surprised that Ancestry mimics life.