So it comes down to who is baptized validly. Would you say a Catholic is baptized validly? Would you say that any Protestants are baptized validly? I think the standard Orthodox response is that Catholic sacraments are nothing. And that Protestant baptism is also nothing. Am I correct? Are there any exceptions to that?
I think this discussion was supposed to be between sedevacantist claims and Catholicism, not Orthodox vs. Catholic
But anyway, for what is worth I don't think Baptism is seen as "nothing"...
The main exception being that in
most jurisdictions, those who have been baptized
in water and very specifically "in the name of the Father, the Son, and the Holy Spirit" in a Church that
affirms the Holy Trinity do not get re-baptized.
I never really grasped the entire notion to be honest. But the underlying assumption is that the Baptism was valid. I am cradle and I've never heard of this before moving to the US...
My wife converted from a denomination that refers to itself as Christian, but their definition of the persons of the Holy Trinity and their "baptism" is profoundly different so she needed to be baptized. I personally know former Catholics who were received with Chrismation alone.
On the other hand, we even recognize emergency Baptism done by a lay person as well... For instance, if a baby appears to be in danger of dying, the practice is for
anyone (if at all possible, not one of the parents) to baptize the baby. If the baby ultimately survives, then the full baptismal service is done, but without submerging in water and the baptismal formula.