It definitely benefits the Church to excude from communion those who offend her unity by denying her teachings or her authority. Lefebvre rejected the rightful authority of the pope to appoint bishops and the rightful authority of an ecumenical council to change the liturgy. Therefore, he deserved to be excommunicated.
The defenders of the SSPX are grasping at straws when they talk about what they thought Lefebvre believed instead of looking at what he actually did.
It definitely benefits the Church to excude from communion those who offend her unity by denying her teachings or her authority.
Have you read
Ecclesia Dei in its entirety, or did you read it the way you read Canon Law? Read paragraph 6c:
"...respect must everywhere be shown for the feelings of all those who are attached to the Latin liturgical tradition,
That's me. Respect my feelings.
by a wide and generous application of the directives already issued some time ago by the Apostolic See for the use of the Roman Missal according to the typical edition of 1962."
The bishops have, in large part, defied this papal directive - to make the Tridentine Mass widely available. If they are in open defiance of the Pope, they are schismatic & excommunicated, by your own definition.