To the writer of the letter, "Scientific theories often taken on faith," there's a huge difference.
Scientific theories are fact. The theory of gravity, the laws of scientific discoveries as in biology, chemistry, mathematics and other applicable studies are factual. Scientific laws that permit us to carbon-date material and manufacture chemicals that allow us to survive illnesses that used to kill us are fact.
Faith plays a part in the way these facts were approached. However, faith in a deity or religion has no basis in fact. It's entirely based on "faith." Faith is believing in the absence of fact.
Let's not confuse believing in some supreme being with the idea that there's a life after death when after all these years, there's absolutely no proof of either. Those who feel the need to believe have that right in this country. Those that know better have that right, as well.