…then those with an opposing view become apostates.
That’s especially true if the topic is one with very high stakes, such as AGW (anthropogenic global warming). Think about it this way: if a person is—(a) convinced that AGW has been proven beyond any doubt (b) threatens life as we know it all over the globe; and (c) can be halted and/or decreased by measures we understand and can control if only we had the will to implement them—then if follow that anyone who disagrees is a person who is endangering life on earth.
Science, of course, is not a religion, and the history of science is littered with theories that have been considered proven and then are disproven. So scientists must remain skeptical and open to any evidence that would challenge their theories and their findings. That’s difficult enough to do when the topic is an abstract one with few practical applications. But when a topic is highly highly politicized (as with AGW), the difficulty increases exponentially and the public also becomes very much involved.