I count Catholics who are members of the Catholic church, and the Catholic vote hasn’t changed, it is still democrat, and it is a religious denomination, not a race, Catholics were voting democrat long before Hispanics showed up in large numbers.
The fact that there has been movement right by the shrinking number of white Catholics in recent years in America, has no meaning about the Catholic vote and it’s continued loyalty to the democrat party.
Again, I think you're trying to make two different points here. In terms of immigration, you are making the assumption that most immigrants are Catholic, when in fact the latest polling seems to indicate that only about a third are.
You point really should be that Catholicism seems to hold a disproportionate appeal among the economically disadvantaged classes, regardless of immigration status.
Your greater point, I think, is that people who self-identify as "Catholic" tend to vote overwhelmingly liberal. That was not really true in the 2012 presidential election, when the Catholic vote exactly matched the general electorate, 50% to 48% for Obama.
On the other hand, in the most recent (2014) election, self-identified "Catholics" voted Republican, 54% to 45%.
The point that you really should be making is that Hispanic Catholics tend to vote liberal in high majorities. Unfortunately, Catholicism is losing its popularity faster among this group than among whites. I suspect that the popularity of the current Latin American Pope may reverse that effect, but your argument is still against immigration in general, not against Catholicism. Unless, of course, you want it to be for some other reason that you're too polite to mention.