The missing options greatly lessen the validity of the poll, as you implicitly assume down-voting has its place. H) Never. I) Never; flag as inappropriate with a reason (sexism, rascism, spam - the list should be limited and must not include references to the intelligence of the poster or the post). I'm with Voltaire.
The quote Peter alludes to is "I do not agree with what you have to say, but I'll defend to the death your right to say it."
Interestingly, it seems it's not a direct quote from Voltaire, rather a comment by S. G. Tallentyre summarizing his attitude:
http://www.voltaire.ox.ac.uk/www_vf/about_voltaire/didnt_say...
"What Tallentyre wrote was: ... Voltaire forgave him all injuries, intentional or unintentional. ‘What a fuss about an omelette!’ he had exclaimed when he heard of the burning (of a book). How abominably unjust to persecute a man for such an airy trifle as that! ‘I disapprove of what you say, but I will defend to the death your right to say it,’ was his attitude now"
I agree with that attitude as well, I identified what I consider only two possibly valid reasons for downvoting, and I usually don't apply them (racism/sexism, which others say would be more appropriately flagged, and "cool story" useless comments, which I try not to flag either).