It's not necessarily about argumentation-- On Reddit, if I saw something I liked, I'd simply upvote it, and let the system take care of the rest. On Hubski, I find myself having read a really well-done comment, and my hand on mouse reflexively starts moving to upvote the comment... and then I realize there is no upvote. And in that crushing maw of indecision and existential angst, an unused portion of my brain slowly struggles to wake up, and it appears my only recourse is to participate in a meaningful conversation, practice good communication skills, offer quality content, try to tell good stories. Shudder to think.
Huh, I consider clicking the circle to add a dot to be a form of upvote. I'll often click the circle on a comment if I like it but I don't feel I have anything to add but anonymous support. What's nice is there is no way to downvote here. On Reddit, I always worried that I'd be downvoted to oblivion, so that stopped me from posting a lot of comments I thought might go against the grain. Here, the worst thing that can happen is no one replies and no one clicks the circle, which might be a little demotivating, but isn't going to cause me any anxiety. I'm happy to get dots and happy to get replies, and if I get neither, I move on and make another comment somewhere else.