Someone's skepticism, knowledge, and careful assessment might lead them to think that a forum post has a X% of being machine generated (as one example scenario). There are big differences between values of 0.1%, 1%, 10%, 50%, 90%, etc, and the resulting impact of the who are involved in that system.
Because of this, it isn't helpful to say, "Oh you should always be skeptical! It doesn't matter if things have changed significantly such that we have more reason to be skeptical now."