I recently read (in Dawkins' The Ancestor's Tale) about the Alu sequence, and went on to read about transposons generally. Having as I do a rather broad definition of life, I concluded that Alu (and others like it) are lifeforms in their own right, although parasitic ones. I found the potential ethical implications somewhat staggering, especially given the need to shut up and multiply those implications by the rather large number of transposon instances in a typical multicellular organism.
I have written out my thoughts on the subject, at http://jttlov.no-ip.org/writings/alulife.htm. I don't claim to have a well-worked out position, just a series of ideas and questions I feel to be worthy of discussion.
ETA: I have started editing the article based on the discussion below. For reference with the existing discussion, I have preserved a copy of the original article as well, linked from the current version.
Agree, and think your changes alter the question I was trying to ask, which is, not whether destroying Xenokudzu Planet would be absolutely unacceptable (as a rule, most things aren't), but whether we'd need a sufficiently good reason.
I think the LCPW for you here is to suppose that this planet is only capable of supporting this xenokudzu, and no other kind of life. (Maybe the xenokudzu is plasma helices, and the 'planet' is actually a sun, and suppose for the sake of argument that that environment can't support sentient life)
So, more generally, let the gain (to non-xenokudzu utility) from destroying Xeno Planet tend to zero. Is there a point at which you choose not to destroy, or will any nonzero positive gain to sentient life justify wiping out Xeno Planet?
So, if I were building a planet-destroying superlaser (for, um, mining I guess) I wouldn't see any particular difference between testing it on Kudzu World or the barren rock next door.