It's used live all the time. Few admit it but a couple that have are Faith Hill and Reba McEntire both of who are good singers without any help.
The creator of Auto-Tune comments "My wife wears make-up, is that evil?"
Faith and Reba wear make-up too.
A singer on the road needing to perform every night, subject to catching a cold, or flu - might need a little help from time to time. If it's a big concert - you bet the promoters want all the insurance they can get. Taking the night off is not an option.
With the extreme pitch shifting starting with Cher - it's just another tool in the hands of the musician. It's up to the musician what effects and how to control them for their sound.
Guitar, keyboards, and bass, have had effects they themselves control. The sound engineer out front has been controlling the singer's effects. Now some singer's get to control their own effects. If they're up to it, then good for them.
There's a lot of festival gigs where you get just a few minutes to setup between bands. These festivals come with their own rental sound system, including their own engineer who will insist on running the sound themselves. They will not have practiced with the band and isn't going to know what effects to kick in at what part of a song. These pedal devices let the singer quickly setup and change the effects on the mic themselves.
This direction in technology is all good in my book.