What are holy wars? Even if you aren't familiar with the term, you are probably acquainted with the concept: Coke vs Pepsi, Xbox vs Playstation, Emacs vs vi, Windows vs Mac, Linux vs BSD, MIT vs GPL. These are wars waged with few facts and many personal invectives, in an attempt to assert moral or technical superiority. Anyone with a lot of experience with holy wars learn to steer clear, for nothing good ever comes out of it. Or does it?
I believe that, even if holy wars may be harmful and ultimately futile, that there's a real reason for fighting (and hopefully, winning) holy wars, similar to the reason why real religious wars are fought: community size.
Imagine the following scenario: there are two competing open source programs, A and B. For realism, feel free to fill in the spots with Emacs or Vim, in whichever order you like. A "wins" the holy war, gaining most, if not all, of the community in the domain of users of A and B. A gains many well-written up-to-date guides and tutorials, while B only has a few, out-of-date guides. A's set of features grows far beyond B and remains just as stable, with many talented developers contributing code while the watchful masses of users reports any bugs. Other programs only support A because so many people use A and very few people use B. Any advantage that B may have is quickly appropriated by A, by its many users; no such speed of adoption exists for B, whose users would be lucky to get an extremely useful feature from A a year later. A has gained immensely, while B has lost immensely. As a user of A, I benefit from every other user of A. Holy wars matter because community size matters.
However, this piece of writing is not meant to encourage readers to begin hurling ad hominem attacks in the nearest forum or mailing list. While it is true that holy wars matter, to the extent of achieving a large community size, there are usually better ways than those in which holy wars are traditionally waged, that is, with personal attacks. One catches more flies with honey than with vinegar, as the saying goes. Here, marketing (of the morally sound variety) is the optimal weapon. Encouraging users to switch to A, presenting hard facts, and helping such new users during the difficult transition period, while neither forcing nor attacking, and allowing for a clear escape route at any time (for software, this amounts to using open data formats and support for exporting and importing data) will lure in many to your cause.