In general, you can conclude that books, articles, videos, and data sources that you find using the library's tools and resources are reputable sources. However, there is disagreement in academia, industries, and professions, and many subjects are open for dialogue and debate. Think about how you'll see two different PhDs on CNN, both from Ivy League universities, with opposing viewpoints about the economy. Just remember that any argument must be supported with strong supporting material: data, analysis, and reason, for example. Or in the case of the Humanities, knowledge and creativity.
Overall, when you find sources using the library, you don't need to do the kind of evaluation that you need to do with sources you find on the Internet. This doesn't mean that everything you find in a library book or article is something you agree with.