Yes of course full knowledge and deliberate consent are also required. As for freedom of conscience, that does not mean a person can decide for themselves what is or is not morally evil. Conscience must be formed in line with Church teachings. There is also the issue of Natural Law, which is written on the hearts of men. The wrongness of the killing of the innocent would seem to be a fairly basic plank of Natural Law.
We need to be careful here not to give the impression that abortion is a crime that can sometimes be justified. It cannot be justified, ever.
If someone was to pose the question, “Is mass murder a mortal sin”, or selling people into slavery, or any other heinous act, then would there be much prevarication about the answer given?
Abortion is the deliberate slaughter of an innocent child, in the place where is should be safe, usually with the cooperation of his/her mother, and with no place he/she can escape to. Abortion is gravely evil and unjustifiable.