Is A Bad Attitude That Bad?

Now, I spend a lot of time thinking about this subject (read: I spend a lot of time convincing myself that I don't need to work on this). In first grade I brought a knife to school with me to protect myself on my 4 block walk home. First grade! Thank God I was in first grade a long time ago when apparently, this wasn't something to expel a kid over.
I told my high school British literature teacher I thought his assignment was "bullshit" and demanded an explanation as to what the point of it was. So yeah, real adorable child.
Over the years, I have toned down my penchant for not filtering my brain to mouth path pretty significantly. Enough to not get fired.
However, I wonder if I need to "mellow out" or if this is actually helping me along in my career.
Pros:
1) The squeaky wheel gets greased. It's very true. When I was working at the front desk at a radio station and the morning DJ got a DUI, upper management fretted over who could cover his show indefinitely. Because I had no experience, no real working track record, but a really persistent whine I got the position. This has actually worked out pretty well for me over the years. If you want something.... ask for it. A lot.
2) People will think twice about trying to salesman you. This is because people with a semi bad/loud attitude are hard to sell. They push back and because of this my boss respects my opinion. Sometimes people in positions of power come up with bad ideas and everyone tells them it's great in the spirit of being positive. I'm convinced that the higher you are in a company the harder it is to get a straight answer from anyone.
3) Repressing is bad for you. I'm a projector. If I'm mad about something, most people within a 5 mile radius will know about it. The upside of this is that in 5 minutes I feel better. It's out and gone, not gnawing away at me for months.
Cons:
3) You will come off as unapproachable. I've found out a lot of things post facto because friends "didn't want to tell me because I'd get mad." Insert promise to do better here.
4) You will be accused of being negative and judgemental. This is the hardest part for me to deal with. I don't usually mean to be negative but I simply cannot take "because" as an answer.

The strange thing is, a lot of the personality traits that our education system seeks to break us of actually can help us in business settings. Do we foster the brat (me) in the class that's always trying to poke holes in the teacher's lectures? I guess not. But at the same time, I'm not so sure that speaking one's mind at virtually all costs is so terrible.