Re: Anger on the mat
This one seems so much like a no-brainer it's almost absurd. I guess I'm rather lucky as the dojo I belong to has a very good training environment. There's no rule to say you have to like everyone you train with but I've never seen anyone get angry or lose control emotionally on the mat. I think it's just understood that it's just not acceptable from anyone. Especially senior students.
While I've only been training in Aikido for about a year, it seems to me there are a couple of warning signs in what you posted about the type of aikido your dojo is teaching.
1) Promoting someone to black belt who cannot control their anger or emotion on the mat seems to me to be a problem. "Victory over one's self" is one of the tenants of Aikido. I could be wrong but I honestly don't think that would happen in our dojo. As a matter of fact I would probably guess that they wouldn't make it past 4th Kyu with an anger problem like you describe. Especially if it has lead to injuries of other students
2) Allowing someone with a known temper problem and history of injuring other students to not only achieve black belt rank but to actually instruct classes is another problem and shows poor judgment on the Sensei's part I'd say. It's inviting disaster.
3) Martial edge does NOT mean Rage or injured Uke's. When training I know which students I can really be aggressive with and which ones require less aggressive practice. I also know which students like to throw aggressively and if I'm working with them and not feeling up to it because of an injury or some other reason I'll let them know before we begin training together that night. There's never a problem. The smart student will use the opportunity to work on some other detail of their technique. The whole premise of Aikido is to protect the attacker isn't it? If you can't control your waza enough to prevent injury to your uke then you need to back off, slow it down and gain more control. Accidents happen but they should be honest accidents. Never the result of a loss of emotional control.
4) Ultimately the Sensei of the school is responsible for everyone there, not just his/her favorite students. Aren't they all his/her kohai? If there is a problem, especially one involving students getting injured, they need to address it.
It just sounds like there's a really bad culture in your dojo and if what you say about things overheard at seminars is true, you may find that your dojo doesn't have a good reputation with others.
You're goal it so study the art of Aikido and it's many techniques and philosophical concepts. Certainly there are many different flavors of aikido out there and it's important to find a "style" that fits your needs. Remember having a martial edge has nothing to do with anger. Actually I'd say it's quite the opposite. If you can't control your own emotions how will you control your opponent? Anger is no different than fear, they both serve to cloud the mind and thus both must be acknowledged as a byproduct of a confrontation and controlled.
Don't quit Aikido, find a better Dojo and feel good about it. There's no shame in it at all.