Earlier quoted context omitted.
It isn't A/B testing that is bad, it is running and/or modifying stuff in the user's computer without their knowledge that is bad. If a site modifies some part of their layout or whatever isn't bad, but a browser installing addons or changing settings to see if it will crash is bad.
Well, it's not like they're hoping it will crash. Presumably they're hoping it won't . Wouldn't it be more irresponsible to deploy to every user without first testing it out?
Experimental/beta channels can have these changes pushed to it, since that's implied by the name, and those people who like living on the edge of new features do so knowingly.
Let the users control their destiny, let the users decide when. That's the hallmark of a trustworthy company.