Both individual tree sites like Ancestry and MyHeritage and collaborative sites like Geni, WikiTree, and FamilySearch have their advantages and disadvantages, but it is my strong belief that the only way to maintain proper privacy for the living is to not put any identifying details about them on _either_ type of site. If you don't want people to find something, don't put it online. All genealogy sites have privacy settings, and I do use those, but what I "hide" behind them are placeholders: usually just a name, sometimes a birth year or decade (just so stuff will sort correctly). And if a living relative is unmarried or otherwise not a "connecting piece", I don't even make a placeholder for him or her. I only keep track of those people in my stricly-offline tree.
Regarding the messes that people can make out of family tree information: these happen on both types of platform, and in some ways, the individual tree messes are worse, because the sites encourage those mistakes to propagate, and then it becomes impossible to fix. For example, there's someone on Ancestry who made my stepmother-in-law into my father-in-law's great-grand-aunt, and now there are at least half a dozen trees on Ancestry that have this extra daughter attached to parents who lived a century earlier than the correct family. I have sent messages to several of the users involved, but have had no response.
The advantage of a collaborative tree is that if you encounter a mess, you can fix it. Whether your fix will "stick" depends on the specific users involved; sometimes, people blindly and persistently copy whatever they have from some source (be that another website or an old genealogy book), especially if there's an easy automated way to do it, and it can take some extended back-and-forth to convince them of their error. On an individual-trees site, you can simply choose to ignore the system's perpetual prompts about the incorrect trees. Annoyance either way, but I feel the collaborative approach is more fruitful in the end.