I think there were some good responses on why people use ancestry, but I want to offer another point that might give you more perspective.
Sources serve only one purpose: to tell you where the information came from. It is nice to have a viewable link that you can view yourself when you have questions about the source, or find a conflicting record and want to compare. But, the purpose is to tell you where you can get the information.
While links are nice, they will eventually be broken. As the database grows, it will become harder to keep all links actively working. Have you ever clicked on a Wikipedia link to find it is no longer working?
Despite the inevitability of links getting broken, all is not lost. If Ancestry disappears, the link will still tell you where to get the information. For example, the census records contain the year, roll and page number where the information can be found. This will remain valid, and you could go to the archives in person and find it. That is the value of a source.