Regardless of whether you think Apple had the right to do what they did, a better question to ask was it the right thing to do. It can not be good business to tick off so many customers. It is certainly not good public relations. Instead of talking about surging sales and great products, the press will be talking about how Apple turned their customers phones into useless bricks and how they have all these outraged customers.
The thing is, they probably didn't have to disable the phones. The hackers were able to make changes without disabling it, do you really think Apple couldn't have done it. Oh, my opinion on it, the phones worked before the update, they didn't after, Apple broke them. And an awful lot of the unlocked phones out there are being used in other countries or areas that do not have AT&T so without the unlocks, these sales would have never happened. Apple benefited from these sales, and happily took their money.
I did not unlock my phone. I have no problem with AT&T. I tried third party apps but didn't really see anything I wanted so I took them off. My phone after the update works fine. I have been a huge fan of Apple but they have made a number of decisions lately that reek of arrogance and a total disregard of some of their biggest supporters. I still love my phone, but Apple has taken the joy away.
I have a feeling that in a week or two, Apple will try to play the hero and come up with something that activates the phones and people will be thanking them for being so kind. Apple will then say "from now on be a good customer and do what you are told."