Definitely not. Rejecting the belief in god(s) is all atheism is with certainty. It says nothing about your stance on other issues. It's very possible for atheists to see religion as an emotional crutch they don't need, but which provides positive psychological support and moral reenforcement for those who do need it. Someone with that stance can still support churches and see them as rightly tax exempt due to their positive impact on people who are different than themselves for which they are important.

Let's be real though: Most probably do oppose churches being tax-exempt and would point to the many negative things about it in history and modern times (from promoting homophobia to hiding pedophilia).