Some vaccinations should be mandatory.
I honestly think that the system which we have implemented right now is the most effective, mandatory vaccination against polio, smallpox and other devastating diseases is a must, and people dying or suffering from easily preventable diseases such as these is criminal.
However this being said, I do not think that it should be mandatory to be vaccinated against every disease for which we have a vaccination. People are far more likely to have allergies and asthma today than 100 years ago, this is because as a society we are becoming increasingly clean, which leads to decrease exposure to external particles and pathogens. The immune system is like any working machine, in order to stay on in working order it must be used, and if we are increasingly decreasing the rate at which we use and expose our immune systems to new pathogens the less well equipped it will be to respond to any threats.
Because of this for non-lethal/debilitating diseases such as the flu or chickenpox I don't believe a vaccine should be mandatory, as allowing exposure to these can lead to a strengthened immune system overall.
Yes, I am aware that vaccination does use the immune system and is in itself an immune booster but this is only for a limited part of the immune system, only helper T-cells actually benefit from vaccination as it allows for early recognition and elimination of pathogens before the person actually shows any signs of infection. However this is only a small part of the immune system and other parts should be used as well.
Thus it is my belief that to prevent the next Spanish-Flu from being 3 times as deadly as it otherwise might be we should not over vaccinate ourselves and allow our immune system to build a general innate defense against all pathogens if it is our decision to put ourselves at risk to do so.