I mean, no one's forcing me to blindly trust programs I run on my own devices. I make a point of only running open source software for this reason. I don't need to inspect the traffic if I can simply read the source code and look for outgoing calls. I won't run Dropbox for this exact reason. Instead I prefer SyncThing, which has no data caps, no central server, and is open source and easy to inspect.

Obviously I'm not actually reading all this source code (who has the time?), but I strongly prefer it to be available, so that I have the ability if desired. Also for reasonably popular stuff the community tends to suss out suspicious activity pretty quickly.

I absolutely do not trust proprietary blobs; they don't get to run on any of my real workstations. I might run them on my Windows install (primarily for games) if I must, and the computer I use for work gets to run anything my company declares that I need (thankfully not much), but I certainly don't trust them.