Yeah, I agree with you. If you have the ability to vote -- and you both care and are decisively opinionated -- and then you don't, then I don't find that to be something that makes a lot of sense. I can empathize with the criticism or frustration one might want to express towards people who do that.
On the other hand, the idea in general of "don't vote, don't participate in discussion" is what I didn't like. And there are a number of people who may find themselves undecided, for example, about certain issues. I think I'm ok with someone who looks at it and says, "You know, I don't really know on this one. Let's see how it plays out. As I learn more and see more, I may start to form a stronger opinion." And I think that's fine, and those people should be absolutely encouraged -- as everyone -- to hop into the discussion at any time of their choosing.
Mostly unrelated note, in my Political Science course I took at college there was some sort of argument made about maximizing voter participation not being an ideal, or something strange and un-intuitive like that. I can't remember the exact context anymore, though...I'll have to try and dig something up about it. It was a pretty mathematically based course, so it wasn't from a philosophical angle. Wish I could remember!