In ecumenical circles, being "in communion" indicates that two factions are close enough in theology to let one side's folks take communion with the other. That's a factor when church have closed communion.
Following that over to the Catholics, taking the Eucharist assumes that you're in communion with Catholic teaching. Folks who aren't on the same page with the Church can thus be seen to be out of communion, thus giving us the term "excommunicate." Note that it doesn't take some sort of grand statement from the Pope or a bishop to do that; publically giving the middle-digit salute to Church doctrine will do that for you.
What about your "cafeteria Catholics" who want to pick and choose which doctrines they like and pass on the ones that they don't like? Here's archbishop of Detroit Allen Vigneron's take on that-
Asked by the Free Press about Catholics who publicly advocate for gay marriage and receive Communion, Vigneron said Sunday: "For a Catholic to receive holy Communion and still deny the revelation Christ entrusted to the church is to try to say two contradictory things at once: 'I believe the church offers the saving truth of Jesus, and I reject what the church teaches.' In effect, they would contradict themselves. This sort of behavior would result in publicly renouncing one's integrity and logically bring shame for a double-dealing that is not unlike perjury."
Vigneron said the church wants to help Catholics "avoid this personal disaster."
In restaurant-speak, the inverse of a-la-carte is table d'hote; that's the package deal, take it or leave it, no substitutions. Folks are supposed to buy into orthodox doctrine; when you disagree with traditional doctrine, the wise person will consider that it might well be the well-hacked view of history might have more insight that what last night's burrito might be telling them.
Vigneron is plugging for more table-d'hote Catholics, rather than the folks the media seem to love who want a side of same-sex marriage and to hold the natural family planning.