>>I still don't understand the logic. If you choose not to be immunised against a particular disease and everyone else has been then to whom do you pose a threat?
>
>Once there is more than 1 person that didn't get a vaccination, there is a threat. Only if there is exactly one person that didn't get a vaccine in the entire world there is no threat to anyone (though we don't know if the vaccine is 100% effective).

Don't think your argument holds up. If you choose not to be vaccinated then you accept the risk of getting the disease. You are still not a problem to those who did choose to be vaccinated.
If, OTOH, the powers that be are aiming for the complete erradication of a disease it's a different story - it pretty much worked for, for example, chickenpox. But it's not going to work for Tetanus so why make it compulsory? The only argument in favour is similar the motor-cyclist/crash-hat argument.

Best,
Viv