If not overdone, I think it is fun. The community will mature at some point in future, but currently the evangelists comprise of not professionals whose jobs are to get these platforms/softwares to more people but passionate fans and contributors who believe in the product and think that their's is the best of them all. It does lead to an unnecessary increase in tension in the community but it also means that those who are involved will be true to their beliefs and contribute to their distro/software/platform in a much more personal and devoted way.

And it is not like commercial software community is never involved with any flamewars. When they do it, they do it for marketing and they do it professionally [1]

[1] http://www.youtube.com/watch?v=k4EbCkotKPU