Making a new version of iOS that doesn't run as well on older devices — that's fine. I understand that iPhone 4 wasn't a priority (but note that in spite of what many people mindlessly repeat, iPhone 4 performance problems were not because of "new animations and effects").
What I have a problem with is:
* pretending that all devices should be upgraded, even though iPhone 4 clearly should not have been included given the abysmal performance,
* disabling downgrades (it's not that they are technically impossible, it's that Apple specifically disabled them after several days),
The goal was to show how unified the iOS ecosystem is: so-and-so-many percent of users upgraded immediately, there is one version to develop for, etc — but I was sacrificed on the way to that goal. That is not OK.
Net result was that for several months my phone was a useless piece of crap, taking forever to do anything, missing taps and swipes, taking screenshots of the lock screen instead of switching on, etc. That is not OK.
In the future, warn me that there are performance problems and that the upgrade is possible, but not advised. And give me the possibility to switch back.
If they cut off support they are evil for making old devices obsolete too quickly.
If they don’t cut off support they get poor performance with an OS that takes advantage of all the performance in the newest models.