A few thoughts:
Training with someone who has such a bad temper that they could injure you is a bad idea.
Training in a dojo where this is overlooked/accepted is dangerous, and a bad idea.
I wouldn't want to train under a sensei who runs things this way.
However...
I think it's super-important to think about anger on the mat in a more naunced way than just saying it's inappropriate. Obviously, yelling at someone, or losing control of yourself so that you end up throwing someone too hard etc., these are bad things. At the same time, I wouldn't say that being angry is inappropriate. One thing I find really valuable in my training is getting the opportunity to work with anger, frustration, confusion, etc. (as well as joy, satisfaction, and all those warm fuzzy feelings). I see training as a way to work with anger. By this I mean feeling it without acting it out, but also without repressing or ignoring it.
An example: I'm training with someone who seems to resist a little too much. They're relatively new to Aikido, and probably they're just trying to give honest ukemi/be realistic. I try and try and just can't make the technique work. I end up starting to get frustrated and angry. Happens, right? At this point, I have lots of options. I could get the sensei's attention, and ask for help. I could just keep trying. I could talk to uke about what's happening. But I'm still angry, and that's not a horrible thing. Letting it get to the point that I'm "quivering with rage", I think that was the quote, that's a bad thing, I think, but just being angry, not the worst thing in the world. Maybe an opportunity to develop patience, and some compassion for others who get angry (ie everyone). It is up to your discretion as far as when to get help from sensei, when to keep trying, when to avoid a dangerous uke, when to change dojos. I'm just saying that I would never expect to always be blissfully happy on the mat, and I wouldn't expect it from my uke either.
This post is getting super-long winded. I'll try to wrap up. Anyway, I'm not saying that you should just stew, but that getting a little angry on the mat, as long as it's not acted out, can be a great opportunity. I realize these comments might not apply to the original post exactly, as that situation seemed physically dangerous, and this is a matter of common sense. The issue of physical harm aside, I thought some posts suggested that you should avoid training with people who have "issues" or make you a little uncomfortable, and this bothers me. I think that as long you feel that you're not endangering yourself physically, you should try to train with everybody in your dojo, not just the people who make you comfortable.