Learn English – the meaning of “being the type to point fingers”

I think this is typically called a "foreshadowing" element or maybe "planting and payoff." It's a staple of James Bond movies -- and it's everywhere in the Back to the Future trilogy.

You could accuse those contributors of being naysayers (Merriam-Webster):

: one who denies, refuses, opposes, or is skeptical or cynical about something ▪ There are always naysayers who say it can't be done.

The part relevant to your intended use is ‘skeptical or cynical about something.’