Yes. Sometimes. It depends on the topic, the participants, my mood, what else is competing for my attention and hopefully, whether or not, I'm reacting or reflecting
A political story with 200 comments? Well that will probably send me into "Someone is wrong on the internet mode," and it really won't matter who is participating, I'm less likely to learn something that's worth knowing and more likely to call someone a moron - and there are more appropriate places on the internet to do that.
A discussion where the people commenting are expressing professional opinions, I'm more likely to read through a significant portion of the comments and more likely to scan all or most of it...though I'll probably not pay much attention to one-liners.
Since threads flow where they flow based on participants, and long threads are often long because the topic drifts as the comments become more deeply nested and generally more interesting to those commenting than those reading, I don't feel any obligation toward reading anything.
Then again, I don't think constructive discussion is necessarily the important goal...constructive expression is. What matters is not exactly that you write something in response to what I write, what matters is if you do something and writing in response is just one form that the doing might take.