Not to kibitz, but this whole automatic dismissal mechanism appears to be an institutional form of the “no true Scotsman” fallacy. It would be like saying any Baptist who unrepentantly drinks or swears or commits a sexual sin is therefore not a true Baptist, and we don’t have to account for their continued claim to be Baptist. Instead of the messiness and heartache of taking ownership of the problem, we could just ignore it.
But in the more conservative Reformed fellowships (and some others), excommunication can never be automatic because it is necessary for the good of the church to consciously and deliberately go through the Matthew 18 disciplinary process. The congregation becomes witness and party to the process, weeps over the brother or sister publically at odds with God, and comes to appreciate the profound danger of trying to keep one foot in the world and the other foot in the church.
But if that Matthew 18 process is abandoned in favor of a quieter, more painless method, and one that yields no tangible quality of punishment, then such punishment is both illusory in nature, and ineffective as a means of educating the churches, and is doomed to fail in changing caviler attitudes towards the high calling of Godly living.
Peace,
SR
Let's kibitz a bit longer. Catholic is a definitional thing. A Catholic is one who is in communion with the Church. Those whose actions and words establish that they are not in communion cannot be or remain Catholic. It is no different than if I were to simply declare myself an NFL quarterback or a Navy SEAL, or Kalif Sheik Mohammed made a statement today saying; "Although I have not changed any of my core beliefs or practices and have not repented of any of my sins I am today declaring myself a Catholic." He would be no more Catholic than Nancy Pelosi.
Many people are very confused by the whole concept of excommunication. It is not always a formal procedure and its purpose is not punitive. Matthew 18:15-17 concerns disputes between Church members, not necessarily sins. However, when we consider that sin hurts not just the sinner, but all members of the Church excommunication can be considered the beginning or recognition of the need of the "Matthew 18" process.
Peace be with you