But this wasn't "allowed" or endorsed by Apple. It was a third-party company doing something underhanded. Is there some reason Dropbox would be more trustworthy on Linux?

I think the "lame overreach" hurts the credibility of the argument--even if it has merit.

It’s a crazy argument from them, considering their licensing allows anyone to do anything they like with a system apart from hide the resulting source code. Policing third parties like Dropbox is actually a strength of a proprietary system, so why bring it up at all?

I could make the claim that GNU software can get you killed, because military organisations build applications on top of it. This is true, but it hardly seems a fair point to make in assessing something like GNU/Linux.

There are legitimate weaknesses and user hostile designs in Apple operating systems, but Dropbox is not one of them.

Edited to add: anyone who remotely cares about security would not allow Dropbox anywhere near their systems, but that’s another discussion!

"Another way of looking at it, is that if it's allowed for dropbox it could be allowed for other apps."

And the same people will cry censorship if Apple tries to enforce anything on Dropbox.