Older members of this forum will recall a time when irons were considered easy to hit and woods were impossible, and there were plenty of little Hitlers (usually including the entire club committee) ready to berate anyone seen teeing off with an iron on anything but a par 3 as it was making the game too easy and thus wasn't the correct form (and if you don't believe me, try getting hold of Michael Green's The Art of Coarse Golf published in the late sixties - there's a wonderful mickey-take of the issue in it). And back then all irons were blades ...
It would be far more accurate to say that cavity irons have a slightly larger sweet spot than blades, but blades aren't exactly difficult to hit. The reality is that some folks like and suit one, some like and suit the other. Some higher-handicap players may suit blades because the harsh feedback from a mis-hit forces them to concentrate on accuracy. Others lack that level of fine motor control to mend their ways and thus will suit cavities better. As with so much in golf, it's a case of horses for courses.
Of course you will always get wiseacres saying that blades are the only irons to play if you're serious about golf. If that's true, then there's a Hell of a lot of pros on the tournament circuit playing cavity backs these guys should be lecturing to, as I guess they haven't heard the news yet.