Consensus is a different concept than Truth.
Consensus can be wrong. "Appeal to Belief" is a common false argument and bias. Although blockchains can be used to verify consensus, they do not inherently have the tools to determine Truth.

The problem with false news stories, propaganda, false marketing, etc. is there intends to take advantage of a victim in order for someone else's gain.

Free speech is wonderful. It allow people to express themselves, provide opinions, submit facts, etc. But we as a society expect Truth in certain circumstances. Think how books in a library are organized. Fiction and non-Fiction. When we want to be entertained, we look to fiction. But when we want to make important decisions, we want Truth. Do you want your doctor to spin a yarn of lies as he tell your prognosis? No. Do you want falsehoods when you watch the news, no. How about a witness in a court of law?

So the problem of people knowingly providing fabrications in the context of expected Truth is a problem. It is a lie.

As great as blockchains are, I don't see it as a tool for logic to determine truth. It can pull in other resources who may have an opinion, can provide support or evidence against. But it in of itself does not have the capacity to tell fiction from non-fiction in broad contexts. However, once the classification is made, it could be a repository of record for where that data should be filed.

Just my 2 cents.