I see no problem with it myself. It's just a tool to assist in getting a good end result.
Think of the situation before tuning software came along. Singers didn't walk into the studio, do one take and that was it. It has always been (and still is) standard practice to do multiple takes and use the best of the bunch in the finished product - often 'comping' together bits and pieces of numerous takes.
Bearing in mind that tuning is only one element of a performance, you may have a perfect take bar one word which is out of tune, it has long been standard procedure to 'punch in' just that word on a subsequent pass. Tuning software merely provides an alternative method to address this situation.
It's also worth considering that an issue with a take might not be apparent until the singer has left the studio. Tuning software helps here too.
Sometimes a singer might be having an bit of an off day, and not be quite up to their usual standard. If that's the day the studio time is booked they're screwed. It doesn't mean that they can't sing. If the studio time was booked a couple of days later their performance may be perfect.
The original point of this thread was to pour scorn on the use of tuning software as an effect, which yes, I personally don't like the sound of, and is seriously overused in my opinion, but the use of it as a tool to get the best possible result out of a vocal performance while retaining it's human character is fine.
As I stated before, the software will not make a singer who can't sing sound realistically like they can.
