ReligiousWars are long-running discussions (debates/arguments/FlameWars) in which there are merits to both sides (so there is never a clear winner) and participants have emotional investment in the issue (so participants are likely to resort to ad hominem attacks). When people who have 5 years of experience running one system attempt to have a discussion with others who have 5 years of experience running another system they are likely to generate much heat.
These are not mutually exclusive. Even the most long-running vi vs Emacs FlameWar will be broken off temporarily so its participants can engage in a Linux vs Windows FlameWar (on the side of Linux, of course).
Time does not settle all ReligiousWars. Some withstand age. The BetaMax vs VHS war is still going strong, despite not only BetaMax having effectively lost in the market (even though it was clearly superior), but both technologies being displaced by optical storage anyway. Others do fizzle out, such as the structured programming vs GoTo war, or the war over implementing systems in assembly language vs highlevel ProgrammingLanguages.