Well, most of those junk texts aren't iMessage and Apple is not your phone carrier, so any rejection would just be a cosmetic thing. The texts would still have to be delivered by your carrier before your OS could do anything about them. You say that's easy, but I feel any added complexity would stop text notifications from being instantaneous, and people would complain about any lag introduced. And we already have a working way to cosmetically filter these messages out and silence the notifications, so why reinvent the wheel? I get that you don't like their implementation, but it works great for a lot of people. If you can mockup something better, submit the feedback to Apple and they might incorporate some ideas into a future version of iOS.