I don't know how dangerous religion is. I don't know how dangerous it is to be wrong-headed in an isolated way. For example, your religious belief may tell you it's bad to be gay. I don't think that opinion (isolated) has much of a dangerous effect. If that's how you feel, are you causing harm to gay people? If you don't vote, if you don't prevent them from living or working among you, it is just an unpleasant aspect of your personality - is that harmful, just to be an unpleasant person? But are you marching, protesting, voting, or spreading your hate to your children? Are you beating anyone to death? Are you purposely not hiring them or letting them rent in your properties, or vandalizing them, or even just walking down the street making horrible remarks to gay people? If you hate something, I think it is very hard to keep that hate a secret, so it will cause harm, even if it is minimal (nonacceptance) compared to heinous (murder and voting and spreading).
Part of me thinks, hey, we all hate something, and I have no serious issue with someone's choice to irrationally hate a group of people. One need not be religious to hate something irrationally, either. Often as not, religion is just an excuse to hate something, not the cause of the hate. I still mostly believe in an individual's right to hate people if they want to, but also in another individual's right to attempt to educate them or expose them to reason. The damage comes in when they teach their children to hate, or prevent this population from enjoying rights like marriage or eating at a restaurant or buying/renting property or having a job or adopting children. Their right to hate should be over-ridden by societal insistence that these people they hate have the same basic rights despite anyone hating them. Certainly, nobody should be beaten to death, that is beyond sick.
What most people seem to do, what I see many atheists do, is the whole "tolerance" thing. I grew up where religion didn't seem like a big deal to anyone, and so it actually surprised me to find out people take any of it seriously. To me, it is like having some Irish heritage, you bring it up every St. Patrick's Day or whatever, but it doesn't consume every aspect of your life. I think they call it C&E Catholics, liberal Christians and Jews, etc., whatever they were raised in, lazy. It seems to give them some light spirituality, they believe in god, but they don't really pay attention to the pope with regard to birth control or what priests are molesting altar boys, etc., they give up something really easy for lent, etc.
Are these people harmful? On one hand no, and another yes. They are not paying attention to the horrors, they are living in sort of a gauzy world where their faith is intact, as lazy as it is, as helpful as it might be at times, they don't worry about what's really happening. They are in denial. "Your criticisms of religion don't apply to me" and hide their heads in the sand. I kind of think that's harmful overall. They're not harmful to others, they don't think there's a problem, and they're not critical thinkers. Their religion resides in a partition of their life, all help to them when they need it, nothing to do with it when they don't. People who just don't feel the need to connect the dots. But: If you're not part of the solution, you're part of the problem.
I tend to think most believers are in this latter group, so the direct harm is caused by a much smaller, but more violent or oppressive group of believers. The larger group is complacent and tolerant. Atheists tend to be divided whether they should be complacent (cowardly? polite?) or address the horrifying aspects of the smaller extremely harmful groups. Although it seems like there are more atheists now than ever, I think analogous to the religions, a larger group of complacent and tolerant and unaware non-believers exist, and at the "extreme" would be the aware and vocal set. So is religion harmful? It censors some atheists from having the guts to address problems too. They compartmentalize their lack of belief as something they thought over once and put in a drawer. It doesn't come up much because they don't bring it up or communicate regarding it. It even tends atheists to marginalize other atheists who do speak out. So the harms of even a liberal, tolerant religious segment of society is that it's gauche to make waves, to recognize and vocalize the obvious problems. It's much better to pretend they aren't there. I would call that maybe a 7.5, no matter how at peace and spiritual or charitable they otherwise are. They are using their religion selfishly, it's a luxury to them to get all the comfort without having any of the awareness, and socializing many atheists to reside in that comfortable ignorance.
Of course, I think it's kind of ass-like to attempt to remove someone's crutch right when they're using it, like a hospital waiting room or a funeral. They don't seem to see any harm in addressing atheists with religious platitudes at such occasions, that makes them asses in crisis situations. They are trying to add comfort to the woeful, so their intentions are alright, which makes it really ass-like to piss on it then also. I think that's a minor but real problem, these airheads go about life really, no critical thinking or awareness beyond their own selfish comfort, saying false things without thinking what they mean or whether they are appropriate. On the scale of being beaten to death or being emotionally kicked in the crotch by a religionist in a time of need, I guess most of them don't beat anyone to death, but perhaps resorting to harassing them to suicide, most of them are more likely to say a stupid thing trying to help. Delusions are just harmful.