Right, they have all your files already, so there's clearly some level of trust.

What if Dropbox has an exploit they're unaware of. Someone finds a whole in Dropbox and boom, now they have accessibility access.

Even if you trust the software vendor, security concerns can cascade.

> and people get along perfectly fine and with less inconvenience shoved in their face running programs without permissions systems aside from a simple admin rights/no admin rights [...]

...For values of "perfectly fine" that include millions of malware slaves on the net, hundreds of millions of stolen passwords, targeted 0 days attacking human rights workers, file-encryptor extortion apps, etc. etc. etc.

> What nefarious and yet undiscovered things

If they're undiscovered, how am I supposed to list them?

As far as discovered things, the permission allows Dropbox to sniff the keyboard and interact with any other application as the user. Add that to unrestricted filesystem access, and the right question to ask is what nefarious things Dropbox can't do.

I prefer to know what the apps I install are going to be doing. To this end, OS-enforced permissions for using various services are a godsend. No program should need "admin" rights. And I should be able to know and control what each app I run can and cannot do. This seems utterly obvious to me. Even if most people dont' care, the tools should be there. There've been more than enough cases where apps have collected information they shouldn't have, whether intentionally or lazily. It baffles me that anyone could seriously make the argument you seem to be making.