Basically because whereas some science will ultimately turn out to be useless malarkey ALL of religion is useless malarkey that we have been dealing with for thousands of years. Worse than not adding value such "babble" has been at various times a bulwark for all sorts of evil men and backwards looking philosophies. Some of us are tired of society being held back for the sake of old men's words given unearned weight by being backed by the weight of lies.