When OS 7 came out, there was a great deal of publicity about it long before it happened so that we were all prepared. The same when OS 10 came out. This is not OS 11, but merely 10.9, and the original message I received did not even make it clear that Maverick was an Operating System, let alone that it was going to damage my set-up. I usually accept upgrades more or less automatically because I used to trust Apple, but then we have seen the iPad that was 4G, but wasn't in Australia, and the Apple map program that had horrifying inaccuracies when it came out, and iPhone 5 that wasn't very much at all, so slowly my trust has evaporated.
Sure I can downgrade, which will take hours and involve lots of saving to external drives and moving stuff back again, but I should have been warned.