On what grounds does the Catholic church reject sacraments of protestant denominations? While there is a wide range of opinion among adult-baptism protestants as to whether a Catholic (or other infant) baptism is or can be considered valid, there seems to be (at least in my experience) a general attitude that Catholic communion and marriage are considered valid by protestants.  That is to say, if a protestant were to visit a Catholic church and participate in the Eucharist (communion), most protestants would not have a problem with this (whether the Catholic church would allow this is another question). And certainly if a couple got married in the Catholic church, and later became protestant, no protestant church (that I'm aware of) would require a re-marriage (then again, if a couple gets married before they are Christian at all, I've never heard of any protestant churches requiring a re-marriage in this case, either).

However, if a protestant couple gets married, then later becomes Catholic, they must be re-married in the Catholic church (or at least this is my understanding!).  And Catholics are not permitted (by the Catholic church) to participate in a non-Catholic communion (with a few possible exceptions?). I don't know if Catholics recognize a protestant baptism, or require re-baptism when a protestant becomes a Catholic. (Related question here)

So my question is:  On what grounds does the Catholic church reject communion, marriage, and (possibly) baptism of protestants?
I believe that @Justin Y's answer to an earlier question of mine has the key to the answer to your question as well.  My question was "What is the doctrinal or Scriptural basis for a central Church authority"

In his answer, Justin stated this:


  A central church authority is a necessary byproduct of believing that
  certain ordinances are necessary for salvation. Ordinances often have
  rules for who can be administered to as well as how it must be done.
  Church authority is a very orderly and efficient way to regulate those
  requirements. The Old Testament is an excellent example of this.
  Notice that churches who put more emphasis on ordinances also have
  more structure (Catholic, Orthodox, and LDS churches, as well as the
  Jewish faith). And it's not just a good way to regulate the
  ordinances, but also a good way to regulate doctrine.


The simple answer is that the Catholic Church, like Orthodoxy, as well as some other denominations, teaches that authority must be ordained, or passed along from someone who has the authority to do so. The entire governing structure of the church is based upon these concepts.  Therefore, ordinances performed by someone who is not authorized to perform them  would be deemed invalid.

In a secular comparison, only accredited schools have the authority to hand out diplomas that are seen as valid.  If I were to hand you a diploma for a Computer Science degree, I doubt anyone would accept it as valid because I don't have the authority to hand out college degrees.  If you were to apply for a job that required such a degree, they would likely require you to get it from an accredited school, because mine is invalid.