This is evidenced by the fact that Dropbox felt the need to apologize and alter their behavior. Largely through HN activism BTW https://techcrunch.com/2016/09/09/dropbox-responds-to-accusa...
They explaining themselves is not evidence of what at all.
Characterizing typical users as unable to understand rooting sidesteps the point that, when the concept is explained to them, most will not be comfortable with software companies doing this.
Are you suggesting that because many of Dropbox's users don't know about the rooting thing, it's justified by their expansion?
I think the important thing is that, were most users to understand the rooting issue, they would be upset. Most users could easily understand it, if explained clearly. This is likely why Dropbox didn't disclose at all until caught -- and now, presumably, has a techie-sounding disclosure instead of "can we 0wn your machine?", if they are even still doing this on Macs.
This goes along with my original complaint about Dropbox: defaults that are ostensibly in Dropbox's interest, but not users'.
The potential security issue isn't big enough to claim it's a problem compared to making it easy to use for most people.