The dictionary definition of religion is that it’s the belief in and worship of a god or gods. So I can’t see how atheism could possibly be considered a religion. It’s completely lacking the core requirement of religion (i.e. belief in god or god’s). But I’m guessing you meant it more in the colloquial sense? As in the behavior of atheists can be fanatical and preachy? In that sense you are probably correct. Some atheists can be just as preachy, dogmatic and fanatical as religious people are, I agree. But I’m always surprised when religious people use the “atheism is a religion” line as a criticism of atheism. By pointing out how the worst aspects religion are sometimes mirrored in atheism aren’t you also exposing religions flaws? It’s an argument that basically says “atheists are just as bad as us”.