Thanks to DtC I think we’ve covered the tread title. Fundamentalist is an incorrect term for atheists, while activist, radical, evangelical {my fav} or militant might be accurate. Man that didn’t take long.
Let’s move on to the secondary and perhaps more complicated question.
I think we see that beliefs do have a sometimes negative impact on the world. If we are under any moral obligation to try and improve that situation,{I think we are} then how do we approach it in an effective manner. Religion , or religious people, also do a lot of good work in the world. Can we separate the belief system from the actions and address the actions?
IMHO it’s a matter of making the individual{s} responsible for their actions and the effect their actions have on others. I don’t care what someone believes {other than hoping they are at least trying to improve themselves} until their beliefs are reflected in actions that impact others. If the impact seems positive, then I applaud the action and it’s results and don’t sweat the details of belief. If the impact is negative then we need to bring this into the light and the forefront of discourse, using universal concepts of honor, justice, human rights, compassion, rather than language specific to religion.