Maybe, but once established they get pretty gross. I'd say if you are drinking beer in pubs and at home you're probably aware of any problems - people usually are - taking them to meetings allows you to identify and fix them.I bet David is thinking...take that yeast to a CBA meeting, i'll soon find an infection
The people who produce the really off beer without knowing it tend to be the ones who don't go to the pub and don't share with anyone else. As the infection builds up - perhaps over many years - they get used to it. Who are we to say they're wrong any more than the rauch beer brewers of Bamberg, the Lambic brewers or the brewers of traditional Burton Ales (* see below). As long as they don't want me to drink it.
And even if it is infected, at least with a dry stout you can just brazen it out and pretend it has had the soured stuff added or have been matured in wood.
* In praise of Traditional Burton Ale (to the tune of There is nothing like a dame)
We've got jugs of foaming ale, we've got lagers bright and clear
We've got kegs and casks and bottles of every sort of beer
We've got hops with spice and perfume, we get dizzy from the smell
What don't we get? You know darned well -
There is nothing like a drain, nothing in the world
There is nothing you can name that is anything like a drain.