It's not a matter of "following his conscience." The disposition of another's soul is not yours or mine to judge, or their worthiness to receive the Eucharist.
Burke's stance has more to do with the scandal that is created by politicians taking positions publicly that contradict Church teaching.
There are likely lots of Catholics who are, wrongly, pro-choice, but they keep their mouths shut, so nobody knows.
Actually 1 Cor 5:1-5 (among others) gives authority to disfellowship someone over 'extreme' sin. Being an unrepentant baby killer falls into extreme sin in my book.