Are you seriously saying that atheists wouldn't resort to attacking institutions that they think are a threat to them?
Based on their personal "Religious Beliefs" or l lack there of..... it's unlikely. Whatever anybody does outside of their personal religious beliefs is all up in the air.
That atheists are more mentally stable somehow? LOL. Sorry, but no. Don't kid yourself like that.
Show me examples where atheists are strapping on suicide vests, blowing up abortion clinics or even churches, or gunning down people, or using car bombs to kill and injure or scare/threaten people in the name of their God or lack there of.... or in order to force people to believe what they believe out of fear...... and maybe I might agree with you...... but since I can't recall any notable amount of Atheists going around and committing violent attacks on other people like religious people do..... generally speaking, it is safe to claim they are more mentally stable as a whole.
There will always be one or two wing nuts in a group..... but while religions have a long list and a long history full of wing nuts doing things in the name of their God(s)...... I'm still waiting to see the list of Atheists out there who have done similar acts in the name of their belief.
Organizing is the first step toward atheism becoming no different whatsoever, including spurring on the mentally unstable.
Organizing people of like-minded beliefs is no guarantee of anything of the sort.... otherwise we'd also be worrying about what those girl guides are really selling door to door...... once you toss in some religious deity we're all supposed to worship, or else.... that's where the problems begin..... since they don't have one to justify any actions that goes against current laws and rights, I think you're stretching the hypothetical a little too much at this stage.
Most of those forceful bible thumping religious type feel it's their duty to meddle in your personal life because they have some obligation to save you..... or if they don't force their beliefs on you or don't sway you to their beliefs in some fashion, they fear punishment from their God(s) in the after life, so they're more inclined to use force, violence, threats and other means of oppression to get people to believe what they believe.
Atheists don't worry about eternal punishment or threats of a horrible afterlife, there is no deity that exists that threatens you with punishment if you don't recruit your quota of new followers..... you believe what you believe and that's it...... and if others don't believe what you believe, you may think they're idiots.... but you're not going to go out and kill the person because of it.
And I'll add too, that the fact is that any organization advertising in an 'us versus them' fashion like you see with some atheist advertising and some Christian advertising, you'll get more and more risk of some lunatic seizing the message and running off on a tangent with it.
It's possible, but none of their advertisements to date (that I've come across so far that is) ever noted it as a mere "Us vs. Them" fashion...... they're just presenting questions and asking people to think about things......
"There probably isn't a God" ~ Isn't telling people there is or isn't without a doubt, nor are there any claims that what they think is probable, is in fact true, nor is it any form of demand for people to believe or think the way they think..... unlike many religious advertisements that dictate what's right and what's wrong in the eyes of god and their religion, and then followed by the punishment one should expect if you don't agree or follow what they dictate.
And even if there was an "Us vs. Them" mentality....... tell me who started that little scenario.
The religious who for centuries, dictated how everybody should live their lives, in church, outside of church and even in our personal lives, regardless of what we personally believe...... it was always the Christian, the Muslim or the Jewish way of doing things, because anybody else who thinks differently are evil, followers of the devil, or out to corrupt you and send you into damnation.
But now that groups of people in recent decades have begun to join together and correct this and stand up for their own rights to determine what they should believe in, how their lives should be run, etc...... suddenly they're creating an "Us vs. Them" situation.
I suppose you would have preferred all of these people to just sit down, shut up and continue to allow religions to dictate how to live their lives and the laws in our societies?
The only time I could see Atheists getting to the point of resorting to violence and oppression like religions have done, is if and when the religions start to imply more forceful tactics on Atheists and further attempt to unfairly oppress their lives..... in that situation, they'd have every right to defend themselves and send some of those tactics back at the religious wing nuts who escalated the situation to begin with.
If religions don't resort to violent or oppressive tactics and allow the situation to remain at just words and debate..... there shouldn't be anything to worry about.