Why is safe to eat some raw or undercooked meats like beef and fish (assuming you're careful), but not chicken? I know that there are bacteria in chicken, but are they in all chicken, or just so many that the only safe thing to do is assume they're all bad? If not, is there any way to get non-dangerous chicken (for say -- chicken sushi)?
You can have raw chicken in restaurants in Japan - it's delicious. Depending on where you live there may be better or worse food safety standards, but there is nothing poisonous about raw chicken itself.
By the way, sushi is a dish with vinegary rice. The raw-meat dish is Sashimi. A picture of chicken sashimi:
You will note that in this photo the chicken is actually not raw but quite rare. The exterior of the chicken flesh is actually seared and cooked through several millimeters.
If it's really really really fresh chicken that's been well-raised and well-handled, sure you can eat it raw. As has been mentioned, chicken sashimi is not unknown. The same applies to pork, another meat we're usually taught to cook thoroughly (historical associations there - pork was long known as a carrier of worms if not properly cooked, but this is less of an issue in modern times with good pork).
You might want to consider long and hard who your guests are before you serve up chicken sashimi at a dinner party though.
In this thread goblinbox makes a disturbing contribution that references a Consumer Reports article stating that 83% of US chickens are contaminated with salmonella and campylobacter.
That's a high enough percentage to scare me away.
Is raw chicken even appetizing to you? The thought of eating chicken sushi makes me queasy, but that just could be because we've been brought up with the knowledge that you don't eat raw chicken.
It has more to do with the industrial food system. If it's coming out of industrial agriculture, I don't think I'd eat any meat raw. If you can find a good local producer that does its own slaughtering, cleaning and packaging you could ask them about it. Their meat might be safe to eat raw. It just depends on where it comes from.
My rule of thumb is: if I can talk to the produce, slaughter and packager then I take their advice, otherwise I assume not safe until cooked.