The Internet and social media have created venue for angry people to lash out at people and beliefs they disagree with under the cloak of anonymity. It's becomes an online "talk radio" like atmosphere.
Having said that there are those who seek to present an intelligent but opposing alternative view when leaving comments.
In some respects it may even enhance readership and more comments. A topical subject oftentimes attracts various opinions!
Nevertheless it's when people stoop to name calling and personal attacks that things get out of hand. Some people love to fight!
There are some people who no longer allow for comments on articles, Youtube pages, and the like. Some people will "close a question" or remove the question/hub entirely if the comments aren't reflective of their own opinion. In other instances however people close a question because one or two people keep extending the string of comments for example on a religious opinion.
After a while the creator of the question simply gets tired of receiving the notifications. To my knowledge few if any people have ever had their minds "changed" after reading anyone's comments on HP.