Well, there's nothing "wrong" with them, in one sense, after all, they are allowed. What's wrong is that they are massively overused and seldom properly trained. They are actually called "extraordinary ministers of the Eucharist," and this is for a reason.
Especially these days, with attendance way down in so many areas, seldom is the congregation large enough to have the use of EM's kick-in. They are to be used when either the congregation is so large that the priest(s) or deacon(s) cannot distrubute the Eucharist in a reasonably timely manner, or when the "ordinary" minister - the priest - is too ill or feeble to be able to handle distribution and the other ordinary ministers (deacon, ordained acolyte) are not present. That's about it for legitimate scenarios for the employment of EM's.
When these scenarios are not present, the use of EM's really constitutes an abuse. This abuse is institutionalized and compounded in this country and elsewhere when EM's are "scheduled" weeks or months in advance, are poorly trained for the task, or - especially! - when they are used and the *priest* sits down while they distribute without him!
Like allowing for communion in the hand, the rise of EM's originated in an abuse, which became so widespread that the Vatican had to allow it as a sort of "damage control." Rome's authority would simply be flouted, and they knew it, so it was blessed off as a practice. But the norms attached have been flouted in the meantime, so I wonder at the initial cave-in sometimes.
Anyway, in a typical parish these days, there isn't one Mass in a hundred where the use of EM's could "even sort" of be justified. They may be on the official books, but they are almost intrinsically an embodied abuse in nearly every case. Besides, they don't really speed things up much anyway, and why can't we have the extra two or three minutes they might save to commune silently with our Lord?