Why so much anger? Common sense.
You mention when you encounter "one" cyclists. I'm not talking about one, I've got no problem with one, two or three. What I've got the problem with is a group of riders who take up the whole lane and you get stuck behind them.
Guess I was never one for people who always had to do sports activities as a group (when it's an "individual" sport), for whatever reason. Sort of like the ski/kayak clubs of the world whose primary responsibility seemed to be running social functions rather than the sport itself. You have some people who like to be a big fish in a small pond by being the group leader of the "pack". You will litterally have 20 cars or so on a regular basis drive miles upon miles with their bikes so people can ride together. Personally, I think they're wussies. Hey, you got a bike, ride it from your house. Why make a social event out of it? Put it to you this way...if you've got to drive your car carrying your bike to ride that bike a shorter distance than your going to drive...well, find another sport or move. Why am I angry? Because it seems like everyone in the city of Winston Salem, North Carolina is driving to Lewisville or River Park to ride their bikes on the roads that I use to get home or go into town and I end up getting behind them, and those people on bikes don't seem to give a crap what space they take up.
Personally, I loved to ride a bike for the sake of riding a bike and pushing myself. Having a road race is one thing, having 10 or more cyclists out for a "fun ride" is something different. You love the sport? Why do you need people around you to participate/practice in it? As mentioned, when I rode, I rode DEFENSIVLY and not like I owned the road. I knew I could get hit very easily. My buddies and me (when we road together) always got into single file when any cars where around us to let them pass us easier. What do mulitple riders do now? Absolutely NOTHING. Hey, it's their road as well and they have every right to be on that road. See, that's the difference. I never thought I had a "right" to use the road for a road bike. I thought when I used the road that it was my duty to make sure that I didn't make an obstical (sp?) for cars.
Heck, why not allow skateboards on the road? How about unicycles?
As far as tractors? Heck, I'm in the country, thus that farmer was here long before me. I'm lucky enough that I don't have to rely upon the land and livestock to make a living. I figure a man riding a tractor on the road is using that road to get to some land he needs to work, and in most cases when I get beind a tractor, it's only for a couple of miles max. As mentioned before, most guys on tractors will try to make room for you to pass as well. Bottom line..people on tractors seem a lot nicer than people on road bikes in my area.