Everybody has an opinion
Here's a perspective from someone who worked in scientific/engineering (not IT) positions in industry. Oddly enough, I was introduced to Macs by BP, which originally used them for user desktops before Windows PCs. We used assorted mainframes and DEC machines for scientific and engineering work, and the minicomputers were replaced by Unix workstations around 1990. Unix had a steep learning curve, but it was also very stable compared to Windows back then. For business applications, PCs replaced the Macs, and after a few more years Linux boxes replaced the Unix workstations for technical work. Both changes were cost-driven: PCs were cheaper than Macs, and Linux machines were cheaper than Unix machines.
Folks working in big companies often have little choice of the hardware and operating system they're made to use, but scientists in academia may have more freedom to choose. Old-time scientific types invested in Unix had two choices when migrating off proprietary (Sun, IBM, H-P, etc.) Unix workstations: Linux or Mac OS X. The Apple logos seen at JPL and the like reflect the choice of Mac OS X. They got to keep the Unix environment they were already familiar with, plus get Microsoft Office and a consistent GUI. IT types may have been more likely to choose Linux, but scientists were less likely to do so because they didn't want to get involved with configuring and tweaking their computers.
I suspect that zealotry often results from defensiveness; folks who are heavily invested in a particular way of doing things will defend their turf loudly when they feel threatened, especially when they're in the minority. It's just human nature.