I’ve always felt that this argument is among the weaker ones to make, especially in an age, like ours, where 900 people are willing to drink poison koolade over some twisted religious conviction. In fact, you can look back quite a ways in time and find many instances of religious fervor driving people to give themselves over to death. Look at the suicide bombers among the Islamics. Personally, I would position this as part of a larger argument that the Catholic Church is an ancient instition without parallel in the world. An unbroken line of apostolic succession, the preservation of the kernal of the faith thru centuries of severe persecutions, etc etc. This way, you make the persecution case, and also frame it within Catholicism. After all, the Protestants often use this argument, too, but have no 2000+ year old Church to prove God’s guiding presence and protection. I’d say that the reality of the Catholic Church is one of the best proofs not only for the existence of God, but also the truth and inerrancy of the Bible.