Spandex cylcists taking over road

On my way to college every day, i am always annoyed at the way the competitive or spandex cyclist allways seem to hog the road, often takin up more space than a truck.
On a busy stretch of road here may be a perfectly good hard shoulder 2 or 3 meters wide but yet they feel the need to cycle right out in the middle of the traffic lane. Most of the time when a group is encountered they cycle 2 or 3 abreast and make no effort to let traffic past. Not only is it awkward and causing an obstruction but very dangerous both for themselves and others. I mean a truck or car coming up against them is often foced to slam on the brakes or swerve out.
Most of the time, even non-agressive beeps to anounce your presence are met by volleys of vile gestures and outbursts of the most irreverend profanity.
They have a right to be on the road of course, but often common sense is not used and to my eye they seem to go out of the way to cause an obstruction. I can understand the theory of cycling 2 abreast so as to force motorists to take notice -safety in numbers but i see no reason why they cannot go in the hard shoulder.
Another thing is they almost never use the cycle lane, in breech of the law. If a cycle lane is provided, you must use it by law.

Another thing is their choice of roads to cycle. Always choose the busiest routes where they casue a huge danger as trucks and such try to overtake. I would never dream of cycling on some of the routes they take. I cycle, but i alwasy stay to quiter, safer routes and practically never go out on National primary routes, just to dangerous.

I once came across a guy in town, fully deck out who was coming against me on the street. Plenty room for us both, but he engaged wild hand waving gestures and telling me to "get the f**k in". What a plonker i thought.

I guess my question is this - why the hell are they so belligerent.