Ivan, you seem like you're really trying to maintain some form of civility, yet you occasionally slip from time to time.  The slowness of your typing doesn't change the fact that you will never know if those 20% are all liberal or conservative or even anarchists.  So if every 1 out of 5 respondents is an unknown, there is no way you are able to have a controlled sample.  Unless of course, those 20% are exactly who you want them to be in order to drive your poll.  I'm beginning to see a Shakespearean theme here as the thought of "The lady doth protest too much, methinks" comes to mind as you swoop in to defend your poll at every moments notice.