Most of parents have expectations imposed on their children (even concering social, moral or religious matters), Dorian father pretty much tried cook his brain so pretty much i was close.
It can be said about every parent in Thedas , what if they will try to use blood magic to force their child to meet their expectations.
Well considering that we don't know what Morrigan planed to do with child if something at all other than just preserve old god soul, we don't know if he had free choice or not.
Well if kid doesn't exist he doesn't have freedom of choice either way if he is alive he may have freedom or not (as i said that is true pretty much for every human).
Comparing ordinary situations to an extraordinary one is a poor argument. Most parents in Thedas aren't mages. And social/religious expectations still allow the possibility of choice, while Kieran had it made for him before he was even born.
It's just as bad as the "a country uses people too" line, considering that people still do choose how they'd like to contribute. More importantly, a mother should never look at her child as an object.
As for what did Morrigan plan for him? "Nothing" isn't the answer, that's for sure. I will quote, "Kieran had a destiny and now it's in Flemeth's hands".
Regardless, the boy was mentally altered in the process and he never asked for that.