I am an atheist as well, and a Daoist; however, I would classify Daoism as a philosophy rather than a religion, since it does not deal with things that must be believed based on faith or cannot be observed.

To answer your question, Daoism does not hold anything as "wrong". It does not dictate what is "moral" and "immoral" like Christianity, Islam, etc. It is a philosophy about what is and the way things are, and seeks to help people live in harmony with that. For this reason it holds great reverence for nature and things natural, not excluding the many mind-altering things found in nature. I know of many Daoists who use weed recreationally.