Petra
People from Britain do visit places like Afghanistan and Pakistan (and I think polio is also found in parts of Africa).
I have taught children/young people who visit relatives in both countries.
Whilst catching polio in the UK is rare it is not impossible and if we stopped vaccinating then one case brought in from abroad could easily become an epidemic, one UK doctors may not recognise or know how to treat, or even be able to treat.
As for the 'amount' of vaccines, the number of diseases we can vaccinate against has increased but at the same time the actual amount of vaccine injected has reduced.
Nothing is without risk, you can die from drinking too much water but we generally think of tap water being safe.
We have more and more people who are imunocompromised due to medical treatment, not just for cancer but treatment for some types of arthritis suppress the immune system and can be taken for decades.
I think not vaccinating is quite a middle class thing, people who think they are educated and do some 'research' and decide not to vaccinate. But in reality they are intelligent people who do not have the medical education needed to make a fully informed choice.
I actually think if you want to increase vaccination rates you don't make them compulsory for school but you do make them the top selection criteria before faith, siblings, LAC etc.
If there is an outbreak of a highly infectious disease then civil liberties will be put on hold, people will be isolated, possibly in their own homes and public places will close.
The Spanish Flu killed millions and restricted people's lives to a huge extent. Some soldiers returning from WWI were isolated on arrival back in Britain, they died not seeing their families.
In 1962 small pox was brought into the UK from Pakistan, the outbreak was as controlled as could be but people still died.