Aikido does provide opportunity to be part of an interaction where blame is useless. In life we often tell ourselves reasons why we are angry and really we are angry because we are angry. So Aikido does provide a way to look at interactions with no blame and thus no reason to become angry.
Wow. I like this lots. May I quote it?
To the original question, I think that aikido is like any other catalyst. It can be the agent of great change, for good or for bad, or it can do nothing much at all. Just like a catalyst in chemistry, it's a matter of whether it comes into contact with the right ingredients. For some people, it seems like all it takes is the realization of how much harm they have the power to do to make them a gentler, less angry person. I think in cases like that, aikido (or another martial art) is simply the catalyst, the vehicle for realization by someone who was already ready to have this epiphany.
Back to what Mary E said about blame, I think for a lot of us, blame and anger and a sense of powerlessness are all intertwined. You can't just let go of them by a simple act of will; you have to become ready to do so. You can't just say, "I am powerful!" and have the fears that drive anger cease to trouble you. You can't just let go of old angers and the old blame habit, even if you tell yourself logically that they harm you rather than helping you. Now, if you step onto the mat with the desire and intention to free yourself of that stuff...well, maybe that's a sign that you're ready to start letting it go. But aikido might not be the best catalyst; it may push the wrong buttons. And even if it's a good change agent for you, you'll still have good days and bad days.
When change for the better happens, we tend to focus on the catalyst as the cause, but it really isn't. There's a guy I've trained with, who came to our dojo about a year ago, full of enthusiasm, couldn't train enough, had various issues and felt that aikido was the key to working through them. And I think it did help with some things. But I think he got swept away by it all, and when it turned out that aikido wasn't the right catalyst for every issue in his life, I think he got disillusioned. He's not training now. I don't know if he'll be back -- if so, I hope he comes with a better understanding of where change comes from.