The main reason is because they are painfully slow and hold everyone up.
I think my biggest gripe is people doing it recreationally. Why inhale copius amounts of pollution in a risky environment, whilst slowing down and irritating people who need to get somewhere when you could just ride through a park/the countryside? I honestly don't really understand that.
People who commute, fair enough, but i don't know why cyclists get surprised that they annoy motorists*. They are just a slow nuisance (although granted this is partly because our roads are mostly not designed for them).
*disclaimer: many car drivers annoy other motorists as well though
I saw something on TV the other day which showed in traffic you're subject to less pollution if you're outside of a vehicle than if you're sat inside one. Basically the pollution gets in the car and builds and builds. There was a filter technology they demonstrated to remove the harmful particulates from the now polluted air inside the car. In short though you're better off being a pedestrian or out in the open air in traffic.
I'm one that owns a car but uses bicycle as my main form of transport to work. It's only a 6.5mile commute so hardly worth getting the car out for. The engine wouldn't even warm up properly in the time it takes to drive me to work. So the car sits on the driveway all week. I am lucky that the route I cycle is relatively quiet and my start time means I don't meet much traffic at all in the morning. I do extend my ride to get this quieter route however as cycling down Hamble Lane doesn't go down with the motorists and the cycle path is pretty shabby. As part of a team at work I've put out survey's to establish what my company could do to encourage more people to walk, cycle, bus, train, car share to work. Anything to basically reduce the amount of cars on the roads. There were many an interesting survey result that showed such a poor attitude. So much selfishness and entitlement.
I'm also one that, whilst not on my road bike to commute and using an MTB with panniers and several lights, still wears functional cycling clothing. I find it more comfortable wearing lycra. I'm as day glow as I can get, just received some lovely fluro Northwave Raptor Artic GTX winter cycling shoes in fluro yellow. I'm pretty sure if I got knocked off though the first thing to be said would be SMIDSY. I do agree with what someone said about front flashing lights on bikes though, they are an annoyance. They don't allow distance to be judged at all well. Also with bike lights getting brighter many a cyclist aren't using their noggin and are setting it for them to see as far ahead as possible which is simply blinding everyone else. I use a Hope R4 on the front which I'm well aware is pretty bright so have it angled down enough for me to still be able to see enough at speed (20mph) but without blinding oncoming traffic.
I hope one day things will change but I don't see it happening. Too many self centered and self entitled numpties out there. I see bad from both sides and I see good from both sides on the road. I've pulled people up at work for not having lights on their bikes. One morning I had someone from my work shout at me to hold on as I overtook in an unlit park asking could I go slower and cycle with them so that they could see where they're going.....Not impressed. They had to put up with a lengthy ear bashing as we cycled along!
The roads are now vastly over crowded with vehicles. I've no idea what the solution is but I'd like to feel safer when I'm out and about cycling. I enjoy the exercise and the fact I'm doing a bit for the environment and causing less road damage etc. Many a reason in the survey results, mentioned earlier, for not cycling were that people would not feel safe on the road on a bicycle. So catch 22 and people stay using their cars. The last thing is that to me as a nation we're becoming fat and lazy, actually we're pretty much there already. So refreshing going to other European countries. The level of activeness is far greater and the people look better for it. It's really noticeable on landing back in the UK. That's a whole other issue though.
Insurance is a tricky one. It comes down to the individuals integrity at the time of an incident. If I were to cause damage to a car whilst cycling and it were my fault I'd pay up. I accept there are those who don't though. I'm pretty confident that there are far more car drivers causing damage to other cars and driving off leaving no details than there are cyclists doing the same! I basically see it as anyone who comes up with reasons why cyclists should not be on the road, i.e. don't pay tax, don't pay insurance, jump red lights etc are typical examples of those with the self centred / entitled attitudes. Now if there was a test to 100% identify these individuals and ban then from using a vehicle on the road we'd be going a long way to solving the over crowded roads situation
These threads are always rinse and repeat, which is a shame as it shows attitudes etc are not changing. Maybe one day...........