A bit hyperbolic – anyone who blows up abortion clinics or forms militias are, by definition, militant, rather than only those who perpetrate mass murder and global wars – but the point is one that merits being made more often:
“A Christian has to be Adolf Hitler to be called militant. All an atheist has to do is write a book.”
Maybe when atheists start forming armed marches through city streets and blowing up churches and mosques, then they may merit the label of “militant”. Until then, anyone who attempts to use it as a smear against outspoken godless folks deserve no more than derision.