It's all too common (and easy) to lump cyclists into one group -- generally (in terms of policy and public opinion) in a way that encourages dislike. Cyclists are like any other subset of the population and it's unfair to any group to judge them based on the actions of others. That being that, I don't pretend that there aren't cyclists out there who misbehave -- I'm personally very aware of it because they're often the cause of me being treated badly by cars/drivers. As a cyclist, the most effective way I've found to combat this is to be courteous where it matters most -- generally by waving/nodding when you are given the go ahead to cross an intersection by a driver who has the right-away (or more generally, shown any courtesy on the road).
Now, that doesn't mean I go out of my way to exude a staid nature on the bike; I'm generally riding as fast as I care to or want to -- but the thing about being on a bike is that speed is (generally) physically governed -- I cannot ride any faster than my body allows. And in most pedestrian settings (i.e. without the presence of significant downhill stretches) this will be between 15 and 30mph (Individual TTs in the TDF will maybe see an avg speed of 30-33mph -- wattage and speed way out of the reach for anyone but the strongest riders on the most advanced machines).
I bring this up to make a point, a dangerous cyclist (i.e. the dudes you see running lights and being jerks with disregard to everyone else) is dangerous but only marginally as compared to a dangerous driver. And this is of course due to the fact that cyclists are limited to pedestrian speeds (30mph going all) and constitute a small fraction of the mass of a car (200lbs:3000lbs+). But they are dangerous (especially to pedestrians -- one reason they should never be riding on sidewalks) nonetheless and I'd love for everyone to show a little more common courtesy.
More than that, however, I wish (more) drivers were aware of how threatening they are in their vehicles (sometimes weapons). Never am I more aware of how fragile the balance of life is as when I'm on my bike with an angry driver alongside me verbally berating me. And this is because riding the bike is not as easy as driving a car in the best of times (neither of which is especially difficult) -- but in the worst of times it's much harder. And your being alongside me with your window down is about as bad as they come. Not only do I have to continue navigating the road I now also have to consider you and your intentions. You might just be someone who wants to get something off their chest and be on the their way (still far better to do it when neither of us are moving). Or you might be one of the others who will only find solace once you've swerved at the me or run me off the road (yes, I have been maliciously run off the road; no, it's not so uncommon). So my senses flare and my defensive instincts kick in any time a car rolls up with something to say because the moment you do you change from being a driver of a car to a potentially dangerous and unpredictable stranger with a weapon. I doubt I'm far from the the only one to feel this way based on how inflammatory these situations routinely become. It doesn't help that the law will generally take the side of the driver or find themselves impuissant due to the fact that cars can and do flee the scene with none the wiser (ever try to get a license plate number down from a fleeing vehicle -- they don't need much distance on you to make it hopeless)
Now that being that, I understand how easy it is to lump individuals in as belonging to "that group". Despite the number of mean spirited drivers I've encountered, they stand out only because we tend to overlook all the others who are good spirited (and thus never give you cause to notice or appreciate them -- in fact i've only been caught off guard with a car rolling up with a pleasantry/compliment two times). I personally suspect that the malicious drivers themselves are repeat offenders and are responsible for the vast majority of encounters (i.e. if there are 10,000 drivers in an area, and 100 events occur it implies 1% of drivers were involved; what's more likely is that a repeat offending driver causes multiple events over a certain route or a time period which means only a fraction of 1% of the drivers are involved).
Which means I should respect you as long as you don't threaten me, and you should respect me provided the same. But let me tell you, it takes just about all my willpower to not rip your head off when you confront me in your car while I'm already giving it my best to be courteous and safe; I do give it my best, though.