Everything I have experienced and been told has taught me five things:
That no dog is ever aggressive if it has been raised well.
That dogs that are prone to snarling and biting most often only ever do so defensively if they feel threatened. It's very uncommon to find a dog that will actively seek out and attack someone, even when they're on their territory. Even dogs that bark a lot are usually soft-hearted creatures that really don't want to bite you.
That temperament will vary wildly in a breed, although breed will often influence behaviour.
And that with a good attitude, some patients, and most importantly a big bag of treats you can get into the heart of any dog.
I can understand a large percentage of pitbulls being hard to keep, but writing them all off is ridiculous.
Or antidepressants worsening suicidal thoughts
To be fair this one is based on a misperception of a real phenomenom: Endogenous depression sufferers, at their worst, are for the most part unable to fulfill suicidal intentions because of a general lack of energy. When you start antidepressive therapy with them, there's a window period in which the suicidal ideation from the depression remains, yet they do have the energy to do it. That's why it's recommended to commit them for the first period of treatment.
It's actually a bit more complex than that. Antidepressants are suppose to increase the "propogation of thoughts" or something like that. From what I was told increasing serotonin will stimulate your brain into thinking with "more areas", or something like that.
The idea is that a depressed person will be stuck in a mental rut, and focus on negative thoughts to the exclusion of others. Antidepressants are supposed to counter this and open up the variety of thoughts you think, but it's not uncommon for a person to find more negative thoughts to think about.
It's tricky, since brain chemistry is something we don't have a clear understanding about, and these things always effect different people differently.
Personally when I went on antidepressants I actually lost energy. I spent all my time crying in bed, and actually slept for ~14 hours a day. I was told nobody who experienced my symptoms should be on antidepressants and was promptly taken off of them.