This is a photo of me taken in 2002:
This is a photo of me taken earlier this year:
One of these depicts me being militant. The other does not. It's fairly obvious yet there are those who seem confused by the meaning of the word.
1. vigorously active and aggressive, esp. in support of a cause: militant reformers.
2. engaged in warfare; fighting.
3. a militant person.
4. a person engaged in warfare or combat.
I can see where #1 may be appropriate to describe some atheists but aggressive seems a bit out of place. We hear militant in the news a lot when describing radical religious and political fringe groups. You might also hear the word passionate used in the same context.
1. having, compelled by, or ruled by intense emotion or strong feeling; fervid: a passionate advocate of socialism.
2. easily aroused to or influenced by sexual desire; ardently sensual.
3. expressing, showing, or marked by intense or strong feeling; emotional: passionate language.
4. intense or vehement, as emotions or feelings: passionate grief.
5. easily moved to anger; quick-tempered; irascible.
#1, 3 and 4 seem to fit a bit better, at least from personal experience. I guess it is easy to see where the two terms can be confused and become easily juxtaposed. So why do we have people and the media calling atheists 'militant' instead of 'passionate'? As I see it, the vocality of ferverent atheists is rather new, at least in America. We're seen as a social minority, stepping out of line against the grain of accepted cultural mores. Perhaps we're seen as something of a threat to the comfy bubble of bullshit that has enveloped a majority of the populous because they don't understand. Threatening things aren't passionate, they're militant.
Militant? Hardly. Passionate? I'd say so.