While proprietary software won't always do things the way you want them for normal applications you could always restrict their permissions, firewall their network and most importantly unless you had a very serious leak built in the data stayed on your own computer, it might be locked up in a proprietary format with software that has forced obsolescence but I always felt the hyperbole was a bit thick. If you buy a CD you buy the mix the artist wanted you to have, you don't get the raw tracks to remix it the way you wanted it to be. Likewise when you buy a closed source game you get the game experience they wanted you to have, not all the source and assets to remake it the way you wanted it to be. All other things being equal it'd of course be desirable, but it's doesn't make it worthless or immoral to buy it without that possibility.
With "Service as a Software Substitution" as RMS calls it or as web services and the cloud as I'd call it you've got no control at all of neither the software nor the data. You can't even do the slightest change in how it works. When they want it to change, it changes and there's nothing you can do to stay on an old version the only thing you could do is to go nuclear and stop using it at all. Getting the data out and over to a competing service is often far worse and more locked up than a proprietary format. And again, they control your data. I'd be far more concerned about all my documents being on a Google Docs server somewhere than in a MS Office document on my disk under my control.
The worst part is really the way you're tied not technically to their service though, but legally. When the iTunes app store tells me they've updated their Terms of Service and asks me to answer yes or no, it's basically "Would you like to continue using your phone as normal or totally cripple all access to new software and updates?" I don't even bother reading it, it's accepting at gunpoint anyway. And I really don't feel it'd be much different with Android and the Play store. It didn't concern me much when it was primarily so I'd have a phone to play Angry Birds on (see above) because I totally don't care where my scores go, but as you start wanting to use it for more serious things it matters but there's really no opting out.
The stupid thing is that I really do like advantages of cloud syncing, I'd just like it to be against my own private server or at least in a local colo of my choice. I don't want to route it through Apple or Google or Facebook or any of the other big megacorporations. But what we need is a solid alternative, not the wailing song of RMS. He could have complained about the lack of a free kernel forever but as long as HURD wasn't an alternative it just didn't matter much until Linux came along and became usable. Give us a real alternative, based perhaps on AOSP or Ubuntu Touch (ugh) and maybe we can turn the tide. P.S. There was a poll here, 90% wouldn't change their online habits one bit after the Snowden revelations - don't assume the general public is with you.