Why would you remove a canonical link?

[Scratch_MM]

Currently, my client's blog makes a duplicate page every time someone comments on a post. The previous SEO consultant told the developer to not put a canonical link directing it to the main blog post. Did taking out the canonical link result in these duplicate pages?

My question is why would she recommend this action?

Is it best to now add in the canonical link in or should we implement a 301 redirect or insert a index: no follow?

Would adding a canonical link keep duplicate pages from happening in the future?

[SparkplugDigital]

Removing the canonical tag would not result in duplicate pages. It is just a tag to give a suggestion to search engines on which page is the canonical version.

For example if there is a duplicate page and it is not easy to 301 redirect and you can't easily get rid of the duplicate, adding the rel canonical tag would tell Google which version is the main version.

Here is a good resource on Rel Canonical Tags: http://www.seomoz.org/blog/complete-guide-to-rel-canonical-how-to-and-why-not