Network capacity problems do NOT trace back to when Apple enabled the feature (which, in turn, was long before AT&T did).
I'm actually glad the first iPhone users had to use email: I consider it a good habit

I'm also glad to have more options (which I hope to never use). And I blame AT&T for their network's failings (MMS and otherwise) but I also know that ANY other (US) carrier would also have had serious problems with iPhone network usage. The iPhone makes things easier to do, and people do them a lot more than ever before. Many of those things use the network. That, not a failing of Apple's, is at the root of the capacity problem with AT&T.