Perhaps one justification for blocking ads is protecting users from personal information harvesting, tracking, and malware delivered through advertising networks. Aside from that, I can't think of a justification.
I actually think it would be good if there were filter lists that whitelisted ads that were not harmful to users in those ways, but that sounds difficult/impossible to fairly maintain, and I doubt anyone else wants it.
4chan doesn't store threads for very long, hence the plethora of third-party archive sites. I doubt they are still storing any useful data from back then.