If we don't quietly accept Sharia Law, Islam requires Muslims to declare jihad against us to force Sharia on our country.
In my opinion this makes Islam completely incompatible with the principles our country stands for. However, one of the things we stand for is freedom of religion, but Islam requires the muslims to convert, kill, or tax all non-muslims. If we did not have PC we would acknowledge this and act accordingly i.e. extra survelliance on mosques, every arabic individual searched at airports etc.
I am afraid that the general populace is so blind to the truth of Islam that one day we could wake up to a new constitutional amendment stating the we are a Islamic country and sharia is the law of the land.