Such an assumption makes no sense for one simple reason - if the Justices were secretly basing their decisions on Church teachings they wouldn't have needed anything more than half of Justice Thomas' concurrence (which only Justice Scalia joined):
Is it significant that the five Supreme Court justices who voted to uphold the federal ban on a controversial abortion procedure also happen to be the court's Roman Catholics?
It is to Tony Auth, the Pulitzer Prize-winning cartoonist for the Philadelphia Inquirer. He drew Chief Justice John G. Roberts Jr. and Justices Antonin Scalia, Anthony M. Kennedy, Clarence Thomas and Samuel A. Alito Jr. wearing bishop's miters, and labeled his cartoon "Church and State."
Rosie O'Donnell and Barbara Walters hashed out the issue on "The View," with O'Donnell noting that a majority of the court is Catholic and wondering about "separation of church and state." Walters counseled that "we cannot assume that they did it because they're Catholic."
I join the Court's opinion because it accurately applies current jurisprudence, including Planned Parenthood of Southeastern Pa. v. Casey, 505 U. S. 833 (1992). I write separately to reiterate my view that the Court's abortion jurisprudence, including Casey and Roe v. Wade, 410 U. S. 113 (1973), has no basis in the Constitution...Of course, this would still overlap with basing their decisions on the Constitution.
The reality is that the Court's 4 "conservative" justices happen to be Catholic. The occasional pairing with Justice Kennedy makes a 4 or 5 justice voting bloc on some issues where the anti-Catholic bigotry would be useless:
And last week, four of the five Catholics were in the court's minority in voting to uphold death sentences in three cases from Texas...Court observers should be above religious attacks and note two additional facts: (1) the federal ban was written to comply with the earlier decision and (2) Justice O'Connor, the "swing-vote" in that case, was replaced by Justice Alito. With the passing of the O'Connor Court, the law is no longer whatever Justice O'Connor says it is.