Comment by pixl97

I think most users that have not ran the systems themselves really have no clue how bad spam really is. It can quickly spiral to the point were 99.9% of the incoming posts on a system are spam, porn where it doesn't belong, or otherwise illegal content. Simply put even if you as the user filter 99.5% of the spam the system is still majority spam.

IP blocks and initial filtering typically make a massive difference in total system load so you can get to the point that the majority of the posts are 'legitimate'. After that bot filtering is needed to remove the more complex attacks against the system.