No one's asking anyone to give up anything, let alone for brand loyalty.

But it's not really fair to say people have to use something either, is it?  Sure, it would be nice to use all the software ever created, but time and money are limited.  I've tried DS and Bryce, and hated them.  So I'm not going to spend any more time or money on them.  I'm sticking with Poser and Vue.  But I'm not going to tell people they're hurting themselves if they don't like Poser or Vue.  Live and let live.