Of course the state can't impose faith on anyone, nor should it try to. But there's a difference between.
1. Making unbelief/heterodoxy/other faiths and worldviews a crime.
2. Making some public expressions of unbelief/heterodoxy/other faiths and worldviews a crime.
For example, if part of your worldview is a belief that people from Leicester are not really people at all and should be made into the slave-drones of the rest of us 'real humans', UK law (rightly) forbids you from practicising your belief in this country. It does not (at the moment, give it time) forbid you from holding that opinion, just from some public acts based on it.
Replace the 'people from Leicester...' bit with one of the below and you start to see how this distinction can be very important for anyone wanting government to be shaped by the bible.
Euthanasia should be legalised.
Abortion is every woman's right.
Homosexual couples should be able to adopt like any other couples.
There's nothing wrong with visiting a prostitute.
The minute anything is criminalised, someone is forbidden from living out all the implications of their worldview/faith on the basis of someone else's worldview/faith. The question for the Christian is whether they'd rather the law-shaping worldview come from the bible or not. Surely, to ask the question is to answer it.