The chicken/egg dilemma is "answerable" - but someone else will always disagree with you (creationists say the chicken, evolutionists the egg).
<i>If you're interested, I'm an evolutionist.</i>
Drawing the line is also difficult - If I showed you the entire visible spectrum, and asked you to pinpoint the exact point where there was a line between red and orange, and you put the line in one place, some guy called Joe Bloggs/John Smith will put the line elsewhere.
Drawing the line between "chicken" and "not chicken" is probably even harder.
It's the same for the combustion/pneumatic debate. No matter how you argue it, some other person will always have a different answer, or a different way of drawing the lines.
I was comparing in the sense that they are both opinions, because expressing an opinion as fact is to say the least, impolite.