Itachi was used by Danzo.If anything Itachi and Shisui were the one's who didn't get used U_U
Itachi was used by Danzo.
Choosing an option when there are no better ones doesn't equate to being manipulated. Especially when you know exactly where you're going to end up in life and now the path you are taking. It's called making a choice and being a shinobi.
In reality Itachi had no choice at all,it was either kill his own clan or be killed alongside them.Danzo did use emotional blackmail to get Itachi to do it though.