I don't think he's talking about only this one issue. Dropbox had an issue with something of this sort recently [0]. They secretly gave their Mac application root privileges. They may have crossed the line for him here. I should say that I'm not speaking for him but I can see how something like this could have been the last straw for someone.
I personally think that the way a company treats it customers is a good display of how good it's culture is. It's not a good sign that they did this.
There was also a time that when you uploaded to Dropbox a file that was already on its servers, instead of storing the new file they stored a reference to the old one (that they already had) as per https://news.ycombinator.com/item?id=2478567
Anyway, there have been other Dropbox issues of a similar nature reported here on HN, and while I haven't been harmed by them personally, it speak to a style of development I don't agree with.
But what finally pushed me over the edge, was this racist initiative at Dropbox. I want no part of that.
https://blogs.dropbox.com/dropbox/2016/12/diversity-at-dropb...
So an implementation-detail for a feature on a platform you don't use caused you to shift to another product, which doesn't even support the feature you are complaining about? Am I reading you correct?
By all means. If you're happy running a FOSS solution on servers you control, more power to you. I'm just confused about your reasoning.