Show you Understand the Issue
Be sure to show that you understand the issue, problem or concern expressed in the article. Ask appropriate questions. A healthy debate is acceptable. A healthy debate is actually going to help the author get rankings, because Google will see that this article is interesting to people and merits some discussion.
I recently did this when one of wonderful members posted an article about dressing cats up for Halloween in cute little costumes. I brought up a healthy debate about how most cats (that I have known at least) despise being dressed up and how demeaning it can perhaps be to the cat. Google likes to see that your content is worth a healthy debate, because that shows you have discussion worth content.
You can say something like:
"I can see your point, but I think ____________ should be something that __________ and therefore, not be an issue when _________________. What do you think?"