There is a sort of anti-religion and anti-pseudoscience zeitgeist in American society, and scientists like Neil deGrasse Tyson and Richard Dawkins make up the figureheads of this movement. The perception is that the rationalist scientific project is under attack by people who try to sell scientifically false statements. Off the top of my head I can name climate change deniers, anti-vaccination activists and creationists as members of a perceived cabal of enemies of scientific progress.
It can be debated whether or not such a cabal really exists or whether its perception is a result of the recent expansion of the reach of ideas and messages made possible by the internet and social networking: perhaps people with wildly differing views are suddenly in contact with one another and are surprised by the variety of opinion out there.
This tweet is not meant to be a philosophically consistent statement concerning the merits of science, but rather a sort of "preaching to the choir" message meant to rally the base against this perceived enemy.