As an Atheist, am I allowed to "witness" in a manner similar to that of Evangelicals?

If you don't believe in a god, then what authority do you have to answer to about witnessing? Obviously not us! Plus you have freedom of speech in the United States to do such a thing just as evangelicals do. I am one of them by the way. Go right ahead, but don't be surprised if we may witness to you in return. Round and around we go!