I'm glad they tested it. I'm glad they ditched it, but I'm glad they tested it. I'd be very surprised if they didn't get something that worked well out of this; such as a new feat/ability, spell or a skill use.
And that is exactly why I'm glad they tried it. It didn't work but now they know why it didn't work (besides the "it's stupid" answer). They know that it has problems at locations A, B and C. It's possible that they thought it would have problems at point D but that D worked well and might be included. Maybe they thought it would work well at point E but it didn't... at all and so now they know to avoid E in the future.
Sometimes knowing why something doesn't work is more valuable than simply knowing it doesn't. New information can bring the designers to look at new directions they didn't look at before or even consider before. If Mearls and Noonan (and the rest) hadn't tried aggro now because it was "obviously" a bad idea we may not have a half-dozen cool fighter feats in the new edition. And even worse, whoever replaces them at some point in the future may add aggro since there wouldn't be the documentation as to why it didn't work in the first place.
So WotC, please - go try new things no matter if the idea comes from TV, movies, literature (both recent and not-so-recent), comic books, anime or video games! Discover why they do and do not work and make D&D even better than it is now!