I agree. While not "harmful", per se, I would argue that this sort of irrationality and magical fairytale thinking negatively affects the quality of life of those who believe it, and in turn radiates out towards the rest of us. You've heard about Harrisburg's mayor calling for a prayer event to fix the budget - it would be no different if she was Wiccan and called for the Wiccan equivalent of a prayer (I don't know a terrible lot about Wicca, so forgive me for not knowing what the equivalent is called). It's not actually solving the problem, so yes, it is harmful to the people it affects.
Anybody who believes in these sorts of irrational things is somehow negatively affecting the world. When one believes irrational things, one accordingly acts irrationally, and our actions affect each other.
I am an ex-pagan and I have a boyfriend who is still pagan. I started that relationship before I became atheist. I generally am turned off by paganism, although some pagan-leaning people have made the initiative to befriend me and they turned out to be allright.
We tend to give paganism a free pass b/c it is not antisexual, not antigay, more concerned with environment. (Although few are antigay, I viewed some rituals as heterosexist with their focus on god and goddess, male and female, etc. It was more like they thought homosexuality was inconsequential.)
I may be a little less angry about it than I was three years ago when I was shunned by my coven due to a conflict with a member who was more popular than me. When I finally met other ex-pagans I found that many had similar experiences.
Pagans proselytize the same as Christians. It's the usual "well our religion is good so it's different if we assume everyone at the party is pagan and talk about how great the goddess is". I've been told to go sit in the kitchen b/c I didn't want to take part in some pagan ritual that someone decided to do at a party and assumed everyone would just love. Some pagans kiss up to atheists, while others have pretty much the same narrative as Christians about atheists thinking they know everything, etc. Pagans who bash Christianity's "stupid beliefs" also annoy me because of their hypocrisy.
I would call paganism/wicca (Jeez, they can't even agree on a name) a "disorganized religion". Organized and disorganized religions both have their sets of problems. Hinduism also fits into this category. I was reading an article about Hinduism that was saying it is more prone to charlatans and cults b/c of its lack of centralization. It is the same, or even more so, with paganism. Anyone who has a magnetic personality can form their own religious clique and manipulate others, especially with the tendency to belief in psychic and supernatural powers. It can be just a high-school clique magnified (cliques become more cliquish when they have a huge process for membership) or it can be closer to an actual cult, and I have known someone who disappeared into a cult.
The belief in harming none is fine. There are other beliefs that have the usual victim-blaming tendency that is common in all religions. The law of three is that if you do something bad, you will get it back threefold. (Think mathematically about the effect this would have on the world!) So according to the law of three, when something bad happens to you, you must have earned it. People do end up absorbing attitudes like this and judging people when they are unfortunate, or blaming themselves.
There are also beliefs that you can change things just by concentrating, doing spells, etc and this is much like prayer. In particular, the belief that just paying attention to the environment will heal it gives a false sense of security and a sense that they don't have to do anything else.