About anger vs plague weapons -- it would seem to me that Mechanical races wouldn't care one way or the other about plague weapons. Being immune to them, they never would have found the distaste for biological weaponry that biological races have, because, to them, it might seem as natural a weapon development as a DUC.
And even beyond that, biological weaponry could simply be seen as a pragmatic and efficient way of both killing an enemy AND demoralizing them at the same time (which it is) by warrior races or exceptionally unemotional or intellectually detached ones.
Hmm -- another idea. Maybe a race follows the principles of entropy in a somewhat abstract way (essentially, they believe in the eventual crumbling and disassociation of matter) -- and they get mad whenever you CREATE a planet, but like you for blowing them up. It'd make you some strange allies, all the while your current ones like you less for smashing entire worlds.
--Chesh
[This message has been edited by CheshireKatt (edited 20 May 2001).]