Look I have and iPhone 5 so I am not in iOS6 but my opinion is whith those who do not want to update.
Yesterday there was Facetime in iOS6, today is not working and I haven't change anything. Who broke Facetime?¿ Any clues? ;P
Come on, Apple fix some things and broke Facetime in iOS 6 and ask everybody to upgrade to IOS 7. Really ? The most advanced company in software can't solve this, right? It is a shame and I support everybody who does not want iOS7, even if for me or you is the best choice.
For example, my mother would be better with her iPhone4 in iOS6, the flat design does not help her.
Some people are arguing about security bugs and holes, well if there is already 80% of people using iOS7, I am pretty sure hackers have already move to iOS7 as it is know that they would target much more devices than iOS 6. Maybe they exploit both of them but who knows, maybe they don't even care for iOS6 now.
Apple didn't break FaceTime. Apple patched a known security flaw in 6.1.5 with 6.1.6. Those that have devices for which Apple actively supports 7 with have had this patch applied with 7.0.4. 7.1 and 7.1.1 have been released since as well.
FaceTime most probably relies on the certificate that tells the app whether or not the latest security update has been applied. When FaceTime is notified that an old certificate is being registered that indicates that the system is insecure and vulnerable to attack and refuses to connect. The solution is to update your software to apply the security patch. Pretty sure FaceTime isn't working for those on 7.0.1 either, and I am pretty sure the solution is to update the software. Do they have a choice to go only to 7.0.4? No, they have to go to 7.1.1 immediately. And is this headline news on Macrumors? Of course not.
I am also pretty sure FaceTime is working on devices unable to update to 7 because Apple provided 6.1.6 to fix the security issue with 6.1.5. The only people this effects are those that stubbornly choose to stay on 6.1.5 and continue to try to access the internet with a gaping hole in the security of their connections.
There is only one device in Apple's line-up that this might affect that was never sold as brand new shipping with iOS 7, and that is the iPhone 4. The 4S still sells brand new today and ships with 7, and the iPad 2 also sold brand new shipped with 7 before it was discontinued. Apple was satisfied that the user experience was at a level that they could stand behind it, and from using both my own iPhone 4S and iPad 2's on 7.1.1 currently I can concur with their judgement on the matter.
Is is slower than on the latest hardware? Yes, but is that not logically expected? Apple have been able to pretty much double the performance of their devices with every iteration, which is astounding. I fully understand those that argue that they want to stay due to performance issues, but there is a trade off between Apple including as many devices as possible in the latest versions of their software, and slight performance issues. They are trying to make as many people happy as they can. This is in stark contrast to other manufacturers, such as Samsung to take a large competitor, that leaves the customer completely on their own when it come to major version software updates. If you would like to be left alone and update your device on your own, Android is a good choice for you. Would those that are taking issue to this be more or less satisfied if Apple instead denied you the possibility of updating to the latest software because your device is 1, 2, or 3 years old??
The point is, there is a perfectly acceptable solution for 99.99999% of the users out there, and for those that freely choose not to utilize that solution it is their choice, and Apple doesn't have any obligation, legal or moral, to offer a different one.
To your other point - if I was a hacker and I was able to use a known security flaw with a known method of attack, that would always be my first target. Why the hell would I spend time and energy trying to find new weaknesses in a new OS when I can simply exploit one I already know about, and I know for a fact that there are still users out there boldly running that OS?