As the man says on many servers there are just an abundance of childish idiots who think crashing is fun.
But when joining a server make sure you don't join in front of any racers, respect the Blue flags, you are not in the race if you weren't on the grid at the start so make sure you let any racers pass you safely.
Try Redline Racing Demo servers if you want good clean racing. We don't allow people to join mid race and if we get any deliberate crashers they are removed fairly quickly.
I'm on most evenings as Redline Quinn (usually after 18:00 UK Time)
Just be sure to read & abide by the rules shown when you join.
You'll also find many people there who can help you with racing/improving times etc...