The OP considered this though, to quote: It's possible that there is a constant decrease in standards, such that every generation is worse than the one before it. But I doubt it. If such a steady decline had been happening since the 8th century BC civilization ought to have collapsed several times over.
A contradiction leaves no doubt. It's not a contradiction then. A contradiction is not just something that is unlikely or infeasible, it is something impossible. It means that your set of beliefs is flawed and that at least one premise needs to be corrected for them to become consistent.
OldSecondHand is correct that it is possible for each generation to have been worse than the preceeding one. For example, the degradation might be so minute, or we may have started from such lofty heights, or the society has become more resilient to the degradation. It is possible, and therefore no contradiction. ...just unlikely.
Which it did, in some ways.