I understand what you guys are saying. My problem is that I do not like to change anything on my side if I'm not sure if it is having a positive effect. I also understand that google needs to be secretive about their algos to make sure that people do not exploit it. I cannot however see a problem if they would tell people that tag pages and related pages may be hurting all of their rankings, not just that of the tag pages.

I personally think this is a bit far stretched considering that Wordpress and other platforms create those tag pages automatically, and that not everyone is a SEO who monitors the latest "trends".

What I would like to know:

How would I go about to block those tag pages? I only need to block them from the index right? Or do they need to be deleted completely?

My site has roughly 18k tag pages, and 10k blog posts. Do you think there could be a negative impact on ranking if I remove the tag pages from the index?