What the article says about untrained guitarists is one hundred per cent true. You're likely to find any schmo who can form three chords standing around the sanctuary strumming . . . and as the article says, not always in tune.
Also a good point that the sound of a guitar is swallowed up in the typical sanctuary. Unless it's miked -- which leads us to another whole problem. I HATE miked music - especially in church, where the building is usually designed for unamplified music. It sounds awful.
The Episcopal cathedral in Atlanta has possibly the worst acoustics of any major cathedral in the country (they ran out of money and put the roof on early - it was supposed to be Gothic but wound up looking kind of Romanesque - the organist used to say, "Welcome to our Squat Church.") The dean has tried all sorts of different electronic arrangements, but nothing works. There are huge dead zones just west of the transept and just east of the narthex where you literally can hear NOTHING, not even your neighbor singing next to you.