People often use ignore for those who are just here to mess around and play narcissistic games, aka a troll who is just trying to get a rise out of people, not people who provide thoughtful, reasonable, plausible and intelligent commentary, no matter which angle they're exploring.
For example, some like to explore all the possible scenarios, based on actual evidence presented so far, and do so within the bounds of reason. Then there are those who just post nonsense like "THOSE EYES" and conclude from that that SW killed her children, and go on to present theories out of thin air for which there is no evidence on the table, like "sleepwalking". Those people you can't really take seriously and people might consider that they add nothing of value to the discussion, hence the ignore button.