The terms "Holy Ghost" and "Holy Spirit" are completely interchangeable. In fact, there have been a few times I've noticed that the Douay-Rheims bible uses the "Spirit" form.
Traditional Catholics generally use the term "Holy Ghost" because it is...traditional to do so in English speaking countries. Also, when speaking to older Catholics I've been told that the Church (in the United States anyway) began the switch from "Holy Ghost" to "Holy Spirit" in the 1950s. One gentleman specifically recalled the reason the priest gave for the change: With the trick-or-treats at Halloween using the ghosts and goblins, the Church doesn't want children to be scared of the "Holy Ghost", and since the word "Spirit" is more gentle, children won't be frightened. Clearly, this is poppycock. I believe the Church in America began using "Holy Spirit" as an ecumenical gesture because it happened (i.e., in the 1950s) around the same time priests and bishops started thinking along ecumenical lines and American protestants always use "Holy Spirit". That's right...the insane ecumenism we generally associate with Vatican II really began to become pronounced prior to Vatican II which is why the American bishops were so active in promoting Religious Liberty at Vatican II.
Thus, today, using one term or another, though each are equally valid can be thought as more a political statement rather than a theological statement. Using "Holy Ghost" signifies to others that one is, or considers himself to be, a traditional Catholic. It tells the world the one rejects the New Order, the New Mass, the New Ecumenism, the New Evangelization, etc., etc., etc. It does not signify sedevacantism or the SSPX or other traditional orders or communities. Even indult traditional Catholics use the term.
Using the term "Holy Ghost", however, does tend to change one's theological outlook. Not because the words themselves have any special psychological meaning or effectiveness, but because one is preferred by theological reformers and revolutionaries in the conciliar structures who have usurped the Catholic Church and have expelled those Catholics who, like Saint Athanasius, cling to tradition rather than fall for the new theology; in his case it was Arianism and in our case Modernism. Thus, using "Holy Ghost" tends to give us a connection with the past and makes us a people set apart.
Interesting that you feel a need to "defend" the use of a fully Catholic term. If you're having to defend using "Holy Ghost", how long do you think it will be before you have to defend using other Catholic terms, such as, "mortal sin", "confession", "true"....