First, they don't just pull you over and make you take a blood test. When the officer comes to the car and asks for license, registration and proof of insurance, he or she is going to engage the person in a converastion. If the officer suspected the the person was driving drunk they will observe the person's speech and note if there is a smell of alcohol on the driver's breath. If the officer smells alcohol or notices slurred speech, he is going to get the driver out of the car and adminster a field sobriety test. Walk in a straight line, recite the alphabet, touch your finger to your nose, follow the pen with just your eyes. If those thest are failed, the officer will then ask a person to submit to a breathalizer or, in this case, a blood test.
See, you left out a whole bunch of steps that are designed to prevent non-drunk people from being dragged down to the station. If the person doesn;t know they are a hemopheliac, well, then it will have to be dealt with as it occurs. If the person does know, there are two other options; breath or urine.
Look, it's just another option for the police officers in the field. If you think they are going to be pulling poeple jsut to try out their blood test kits you are insane.