Freedom of belief is vital, but freedom to be left alone without criticism of your belief only fully works if you are able to live an isolated life - hermits can believe what they like with no consequences for the rest of the world. But in a democracy what you believe can dramatically change the lives of others.
The racist views of the BNP are one example, and widespread fear of difference can lead to mainstream parties trying to resist the BNP by making xenophobic noises. Another awful example is the serious rise in diseases like measles and whooping cough because of the belief that certain vaccines were harmful. That kind of belief can lead to disability and death of others, and it's a moral failure to sit back and insist that such beliefs are merely personal matters.
Creationist views deeply change the way people view the world. In countries like the USA, they lead to a widespread belief that global warming need not be dealt with because God made promises in the Bible. Such views could lead to the deaths of tens if not hundreds of millions in generations to come.
Science is about doing our best to find out what is actually true, and it's neither arrogant or pompous to work hard to educate people about what science finds when it impacts our lives and the lives of those of future generations. In the long term, that education (or lack of it) will be the only thing that matters.