hought experiment: imagine a planet with a xenobiology that only supports plant life - nothing sentient lives there or could do so - and there is (let us assume) no direct benefit to us to be derived from its existence. Would we think it acceptable to destroy that planet?
I think this scenario is a little difficult to visualize- an entire biosphere we can't derive a benefit from, even for sheer curiosity's sake? So, applying the LCPW: the planet has been invaded by a single species of xenokudzu, which has choked out all other life but is thriving merrily on its own (maybe it's an ecocidal bioweapon or something). Would it be acceptable to destroy that planet? I'd say yes. Agree / disagree / think my changes alter the question?
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.
which has choked out all other life
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 sent...
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.