It depends on the situation.
For example, I am a Pagan. I have several friends that are also Pagan, but I have at least one friend that is devout Christian and I also have a friend that is a strict Atheist.
People wonder how we get along. It's very simple. My Atheist friend and I have had many conversations. He respects my views because I realize that my religion is based in belief and not in scientific fact. I am comfortable with the idea that my religion is a set of stories to explain various things, and that they may not be spiritual fact. He also has respect for my views that, one can learn MANY things from religion without being Theistic. Just as one can learn from reading Aesop's fables without believing in them literally.
Our Christian friend, well he believes in the Bible. He also believes that Science proves creation in many ways. This can lead to various "Facepalm" moments. However, he is not trying to push his beliefs down our throats, therefor there is no reason to be militant or do the same. He is a very intelligent person in every other way, his beliefs are his own and they stay that way. He is also a bisexual and doesn't believe in oppression of any person for any reason.
In the above examples, being militant to someone that acts in this way would be self defeating. It would do nothing but make all Atheists seem like militant Douchenossles that are intolerant of others' beliefs and convinced of their own mental superiority. Which would be even funnier if there were ever a scientific discovery that proved even one point of arguments used by the Theists (Let's not say it's not possible. You never know, we can only speak of what we know now.)
Now if people try and shove their beliefs down your throat? Yeah let 'em have it if you really want. Realize, however, that it probably won't make things better. Likely it will do the opposite.
So to sum it up, I say be respectful or silent in most situations. There is rarely a reason to be militant about it, and even if there is cause to attack someone's beliefs... well it likely won't help anything anyway.