I suggest you watch Judgment Day: Intelligent Design on Trial
Athiests become vocal against religion because religion leads us to an intellectual dead-end. An end where we lose our ability to find new technology, medicines, and answers. Where exploration and education stops, and everything is replaced by believing what you are told to believe. Look no further than the middle east to see where religion leads us. It was the scientific revolution that brought us to where we are today, and certainly not religion.
There are those that would put an end to the quest for knowledge and understanding of ourselves. True, not every christian or religious person is extreme - but decent people, following the leadership of a clergy are quick to do the wrong thing - and think nothing of it.
The residents of Dover thought they were doing the right thing - using public funds to teach religion in school, and selecting science textbooks that were intentionally out of date, and light on legitimate biological science. If religious fundamentalists had their way, progress in biological sciences would stop. Books would be burned, and America would become scientificly obsolete within just a few decades.
All so people can feel comfortable with in their bronze-age understanding that the world is 6000 years old, and that man is made in the image of God - rather than a lower primate.
It's not purely a matter of 'what is to be gained' - it's a matter of 'what could be lost'.
- Lime