Depending on your commitment to training, it will take around 5 years to work your way through the syllabus and condition yourself for the gradings.
Everyone has the opportunity to be an instructor, not all black belts are instructors but all instructors are black belts.
Simply put...Yes but in a good way, you cannot possibly expect to train in any combat based martial art and not get bruised, its all part of conditioning.
Getting injured on the other hand is entirely different and if you listen to instructors and train well with your partners injuries rarely occur and can be avoided.
Nobody is forced to take gradings or even participate in gradings...however it is one of the few ways to really test yourself & your knowledge and it is really the only way to progress through the syllabus.