You may know that a 2013 study concluded that comments influenced the reader’s understanding of an article. Lastly, I have read comments from many websites of different news websites and I have found that the information quality in those comments was most of the time very poor.
Trolling
Whatever the subject, there are trolls who write text that has no value. On one hand, the authors perform research to write high quality articles. On the other hand, some trolls destroy this valuable information by writing stupid statements at the bottom of the article. The troll contents may modify the opinion of readers and mislead them even if they are acceptable. For example, you write an article saying that sugar makes you get fat using medical studies as reference. Then, below your article, someone may tell you that there are good and bad sugar. You may think it is an acceptable comment for a debate but from a scientific point of view it is not true. It also does not add any value to the article.
Here is another example: A well known said that it was dangerous to envisage to get pregnant after 45 years old. Below the said article a woman said it was possible thanks to medicine to have a baby when a woman is 50+
I have found that “trolling” is THE major issue of comment sections today. There are comments that are full of allegations, prejudices, stereotypes. Furthermore, comments require moderation and moderation cost time and perhaps money.
Undercover advertisements
Undercover marketers advertise their products by posting fake comments about a product or a service. By doing so, they influence the readers and the author of the blog. However, they can mislead the readers by telling big lies about a product. Even if an article talks about the weaknesses of a product, the comments can persuade people to buy it even if it would be a major mistake.
Spam bots
Spam bots always try to post fake comments. They pressure your web server by sending many queries. If you rent a dedicated server or a VPS and if you investigate, you will discover that most of your traffic comes from spam bots if you have a comment section.
My opinion
In this context, moderating useless comments are a waste of time. It is a new form of spam. It has no value and it is useless for your website. Some people say that comments are good for SEO. I have no proof that a long text will bring more traffic. Quality is more important than quantity. People don’t understand that on a page you put on the same level high quality text and poor quality text. However, when you write an article, you can add quality text whenever you want to get more words.
Forums are better than comments section.